Rest of the merge.

[linux-2.6/linux-mips.git] / fs / namei.c

/*
 *  linux/fs/namei.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

/*
 * Some corrections by tytso.
 */

/* [Feb 1997 T. Schoebel-Theuer] Complete rewrite of the pathname
 * lookup logic.
 */

#include <linux/mm.h>
#include <linux/proc_fs.h>
#include <linux/smp_lock.h>
#include <linux/quotaops.h>
#include <linux/pagemap.h>
#include <linux/dcache.h>

#include <asm/uaccess.h>
#include <asm/unaligned.h>
#include <asm/semaphore.h>
#include <asm/page.h>
#include <asm/pgtable.h>

#include <asm/namei.h>

/* This can be removed after the beta phase. */
#define CACHE_SUPERVISE /* debug the correctness of dcache entries */
#undef DEBUG            /* some other debugging */


#define ACC_MODE(x) ("\000\004\002\006"[(x)&O_ACCMODE])

/* [Feb-1997 T. Schoebel-Theuer]
 * Fundamental changes in the pathname lookup mechanisms (namei)
 * were necessary because of omirr.  The reason is that omirr needs
 * to know the _real_ pathname, not the user-supplied one, in case
 * of symlinks (and also when transname replacements occur).
 *
 * The new code replaces the old recursive symlink resolution with
 * an iterative one (in case of non-nested symlink chains).  It does
 * this with calls to <fs>_follow_link().
 * As a side effect, dir_namei(), _namei() and follow_link() are now 
 * replaced with a single function lookup_dentry() that can handle all 
 * the special cases of the former code.
 *
 * With the new dcache, the pathname is stored at each inode, at least as
 * long as the refcount of the inode is positive.  As a side effect, the
 * size of the dcache depends on the inode cache and thus is dynamic.
 *
 * [29-Apr-1998 C. Scott Ananian] Updated above description of symlink
 * resolution to correspond with current state of the code.
 *
 * Note that the symlink resolution is not *completely* iterative.
 * There is still a significant amount of tail- and mid- recursion in
 * the algorithm.  Also, note that <fs>_readlink() is not used in
 * lookup_dentry(): lookup_dentry() on the result of <fs>_readlink()
 * may return different results than <fs>_follow_link().  Many virtual
 * filesystems (including /proc) exhibit this behavior.
 */

/* [24-Feb-97 T. Schoebel-Theuer] Side effects caused by new implementation:
 * New symlink semantics: when open() is called with flags O_CREAT | O_EXCL
 * and the name already exists in form of a symlink, try to create the new
 * name indicated by the symlink. The old code always complained that the
 * name already exists, due to not following the symlink even if its target
 * is nonexistent.  The new semantics affects also mknod() and link() when
 * the name is a symlink pointing to a non-existant name.
 *
 * I don't know which semantics is the right one, since I have no access
 * to standards. But I found by trial that HP-UX 9.0 has the full "new"
 * semantics implemented, while SunOS 4.1.1 and Solaris (SunOS 5.4) have the
 * "old" one. Personally, I think the new semantics is much more logical.
 * Note that "ln old new" where "new" is a symlink pointing to a non-existing
 * file does succeed in both HP-UX and SunOs, but not in Solaris
 * and in the old Linux semantics.
 */

/* [16-Dec-97 Kevin Buhr] For security reasons, we change some symlink
 * semantics.  See the comments in "open_namei" and "do_link" below.
 *
 * [10-Sep-98 Alan Modra] Another symlink change.
 */

/* In order to reduce some races, while at the same time doing additional
 * checking and hopefully speeding things up, we copy filenames to the
 * kernel data space before using them..
 *
 * POSIX.1 2.4: an empty pathname is invalid (ENOENT).
 */
static inline int do_getname(const char *filename, char *page)
{
        int retval;
        unsigned long len = PAGE_SIZE;

        if ((unsigned long) filename >= TASK_SIZE) {
                if (!segment_eq(get_fs(), KERNEL_DS))
                        return -EFAULT;
        } else if (TASK_SIZE - (unsigned long) filename < PAGE_SIZE)
                len = TASK_SIZE - (unsigned long) filename;

        retval = strncpy_from_user((char *)page, filename, len);
        if (retval > 0) {
                if (retval < len)
                        return 0;
                return -ENAMETOOLONG;
        } else if (!retval)
                retval = -ENOENT;
        return retval;
}

char * getname(const char * filename)
{
        char *tmp, *result;

        result = ERR_PTR(-ENOMEM);
        tmp = __getname();
        if (tmp)  {
                int retval = do_getname(filename, tmp);

                result = tmp;
                if (retval < 0) {
                        putname(tmp);
                        result = ERR_PTR(retval);
                }
        }
        return result;
}

/*
 *      permission()
 *
 * is used to check for read/write/execute permissions on a file.
 * We use "fsuid" for this, letting us set arbitrary permissions
 * for filesystem access without changing the "normal" uids which
 * are used for other things..
 */
int permission(struct inode * inode,int mask)
{
        int mode = inode->i_mode;

        if (inode->i_op && inode->i_op->permission)
                return inode->i_op->permission(inode, mask);
        else if ((mask & S_IWOTH) && IS_RDONLY(inode) &&
                 (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
                return -EROFS; /* Nobody gets write access to a read-only fs */
        else if ((mask & S_IWOTH) && IS_IMMUTABLE(inode))
                return -EACCES; /* Nobody gets write access to an immutable file */
        else if (current->fsuid == inode->i_uid)
                mode >>= 6;
        else if (in_group_p(inode->i_gid))
                mode >>= 3;
        if (((mode & mask & S_IRWXO) == mask) || capable(CAP_DAC_OVERRIDE))
                return 0;
        /* read and search access */
        if ((mask == S_IROTH) ||
            (S_ISDIR(mode)  && !(mask & ~(S_IROTH | S_IXOTH))))
                if (capable(CAP_DAC_READ_SEARCH))
                        return 0;
        return -EACCES;
}

/*
 * get_write_access() gets write permission for a file.
 * put_write_access() releases this write permission.
 * This is used for regular files.
 * We cannot support write (and maybe mmap read-write shared) accesses and
 * MAP_DENYWRITE mmappings simultaneously. The i_writecount field of an inode
 * can have the following values:
 * 0: no writers, no VM_DENYWRITE mappings
 * < 0: (-i_writecount) vm_area_structs with VM_DENYWRITE set exist
 * > 0: (i_writecount) users are writing to the file.
 *
 * WARNING: as soon as we will move get_write_access(), do_mmap() or
 * prepare_binfmt() out of the big lock we will need a spinlock protecting
 * the checks in all 3. For the time being it is not needed.
 */
int get_write_access(struct inode * inode)
{
        if (atomic_read(&inode->i_writecount) < 0)
                return -ETXTBSY;
        atomic_inc(&inode->i_writecount);
        return 0;
}

void put_write_access(struct inode * inode)
{
        atomic_dec(&inode->i_writecount);
}

/*
 * "." and ".." are special - ".." especially so because it has to be able
 * to know about the current root directory and parent relationships
 */
static struct dentry * reserved_lookup(struct dentry * parent, struct qstr * name)
{
        struct dentry *result = NULL;
        if (name->name[0] == '.') {
                switch (name->len) {
                default:
                        break;
                case 2: 
                        if (name->name[1] != '.')
                                break;

                        if (parent != current->fs->root)
                                parent = parent->d_covers->d_parent;
                        /* fallthrough */
                case 1:
                        result = parent;
                }
        }
        return dget(result);
}

/*
 * Internal lookup() using the new generic dcache.
 */
static struct dentry * cached_lookup(struct dentry * parent, struct qstr * name, int flags)
{
        struct dentry * dentry = d_lookup(parent, name);

        if (dentry && dentry->d_op && dentry->d_op->d_revalidate) {
                if (!dentry->d_op->d_revalidate(dentry, flags) && !d_invalidate(dentry)) {
                        dput(dentry);
                        dentry = NULL;
                }
        }
        return dentry;
}

/*
 * This is called when everything else fails, and we actually have
 * to go to the low-level filesystem to find out what we should do..
 *
 * We get the directory semaphore, and after getting that we also
 * make sure that nobody added the entry to the dcache in the meantime..
 */
static struct dentry * real_lookup(struct dentry * parent, struct qstr * name, int flags)
{
        struct dentry * result;
        struct inode *dir = parent->d_inode;

        down(&dir->i_sem);
        /*
         * First re-do the cached lookup just in case it was created
         * while we waited for the directory semaphore..
         *
         * FIXME! This could use version numbering or similar to
         * avoid unnecessary cache lookups.
         */
        result = d_lookup(parent, name);
        if (!result) {
                struct dentry * dentry = d_alloc(parent, name);
                result = ERR_PTR(-ENOMEM);
                if (dentry) {
                        result = dir->i_op->lookup(dir, dentry);
                        if (result)
                                dput(dentry);
                        else
                                result = dentry;
                }
                up(&dir->i_sem);
                return result;
        }

        /*
         * Uhhuh! Nasty case: the cache was re-populated while
         * we waited on the semaphore. Need to revalidate, but
         * we're going to return this entry regardless (same
         * as if it was busy).
         */
        up(&dir->i_sem);
        if (result->d_op && result->d_op->d_revalidate)
                result->d_op->d_revalidate(result, flags);
        return result;
}

static struct dentry * do_follow_link(struct dentry *base, struct dentry *dentry, unsigned int follow)
{
        struct inode * inode = dentry->d_inode;

        if ((follow & LOOKUP_FOLLOW)
            && inode && inode->i_op && inode->i_op->follow_link) {
                if (current->link_count < 32) {
                        struct dentry * result;

                        current->link_count++;
                        /* This eats the base */
                        result = inode->i_op->follow_link(dentry, base, follow);
                        current->link_count--;
                        dput(dentry);
                        return result;
                }
                dput(dentry);
                dentry = ERR_PTR(-ELOOP);
        }
        dput(base);
        return dentry;
}

static inline struct dentry * follow_mount(struct dentry * dentry)
{
        struct dentry * mnt = dentry->d_mounts;

        if (mnt != dentry) {
                dget(mnt);
                dput(dentry);
                dentry = mnt;
        }
        return dentry;
}

/*
 * Name resolution.
 *
 * This is the basic name resolution function, turning a pathname
 * into the final dentry.
 */
struct dentry * lookup_dentry(const char * name, struct dentry * base, unsigned int lookup_flags)
{
        struct dentry * dentry;
        struct inode *inode;

        if (*name == '/') {
                if (base)
                        dput(base);
                do {
                        name++;
                } while (*name == '/');
                __prefix_lookup_dentry(name, lookup_flags);
                base = dget(current->fs->root);
        } else if (!base) {
                base = dget(current->fs->pwd);
        }

        if (!*name)
                goto return_base;

        inode = base->d_inode;
        lookup_flags &= LOOKUP_FOLLOW | LOOKUP_DIRECTORY | LOOKUP_SLASHOK;

        /* At this point we know we have a real path component. */
        for(;;) {
                int err;
                unsigned long hash;
                struct qstr this;
                unsigned int flags;
                unsigned int c;

                err = permission(inode, MAY_EXEC);
                dentry = ERR_PTR(err);
                if (err)
                        break;

                this.name = name;
                c = *(const unsigned char *)name;

                hash = init_name_hash();
                do {
                        name++;
                        hash = partial_name_hash(c, hash);
                        c = *(const unsigned char *)name;
                } while (c && (c != '/'));
                this.len = name - (const char *) this.name;
                this.hash = end_name_hash(hash);

                /* remove trailing slashes? */
                flags = lookup_flags;
                if (c) {
                        char tmp;

                        flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
                        do {
                                tmp = *++name;
                        } while (tmp == '/');
                        if (tmp)
                                flags |= LOOKUP_CONTINUE;
                }

                /*
                 * See if the low-level filesystem might want
                 * to use its own hash..
                 */
                if (base->d_op && base->d_op->d_hash) {
                        int error;
                        error = base->d_op->d_hash(base, &this);
                        if (error < 0) {
                                dentry = ERR_PTR(error);
                                break;
                        }
                }

                /* This does the actual lookups.. */
                dentry = reserved_lookup(base, &this);
                if (!dentry) {
                        dentry = cached_lookup(base, &this, flags);
                        if (!dentry) {
                                dentry = real_lookup(base, &this, flags);
                                if (IS_ERR(dentry))
                                        break;
                        }
                }

                /* Check mountpoints.. */
                dentry = follow_mount(dentry);

                base = do_follow_link(base, dentry, flags);
                if (IS_ERR(base))
                        goto return_base;

                inode = base->d_inode;
                if (flags & LOOKUP_DIRECTORY) {
                        if (!inode)
                                goto no_inode;
                        dentry = ERR_PTR(-ENOTDIR); 
                        if (!inode->i_op || !inode->i_op->lookup)
                                break;
                        if (flags & LOOKUP_CONTINUE)
                                continue;
                }
return_base:
                return base;
/*
 * The case of a nonexisting file is special.
 *
 * In the middle of a pathname lookup (ie when
 * LOOKUP_CONTINUE is set), it's an obvious
 * error and returns ENOENT.
 *
 * At the end of a pathname lookup it's legal,
 * and we return a negative dentry. However, we
 * get here only if there were trailing slashes,
 * which is legal only if we know it's supposed
 * to be a directory (ie "mkdir"). Thus the
 * LOOKUP_SLASHOK flag.
 */
no_inode:
                dentry = ERR_PTR(-ENOENT);
                if (flags & LOOKUP_CONTINUE)
                        break;
                if (flags & LOOKUP_SLASHOK)
                        goto return_base;
                break;
        }
        dput(base);
        return dentry;
}

/*
 *      namei()
 *
 * is used by most simple commands to get the inode of a specified name.
 * Open, link etc use their own routines, but this is enough for things
 * like 'chmod' etc.
 *
 * namei exists in two versions: namei/lnamei. The only difference is
 * that namei follows links, while lnamei does not.
 */
struct dentry * __namei(const char *pathname, unsigned int lookup_flags)
{
        char *name;
        struct dentry *dentry;

        name = getname(pathname);
        dentry = (struct dentry *) name;
        if (!IS_ERR(name)) {
                dentry = lookup_dentry(name, NULL, lookup_flags);
                putname(name);
                if (!IS_ERR(dentry)) {
                        if (!dentry->d_inode) {
                                dput(dentry);
                                dentry = ERR_PTR(-ENOENT);
                        }
                }
        }
        return dentry;
}

/*
 * It's inline, so penalty for filesystems that don't use sticky bit is
 * minimal.
 */
static inline int check_sticky(struct inode *dir, struct inode *inode)
{
        if (!(dir->i_mode & S_ISVTX))
                return 0;
        if (inode->i_uid == current->fsuid)
                return 0;
        if (dir->i_uid == current->fsuid)
                return 0;
        return !capable(CAP_FOWNER);
}

/*
 *      Check whether we can remove a link victim from directory dir, check
 *  whether the type of victim is right.
 *  1. We can't do it if dir is read-only (done in permission())
 *  2. We should have write and exec permissions on dir
 *  3. We can't remove anything from append-only dir
 *  4. We can't do anything with immutable dir (done in permission())
 *  5. If the sticky bit on dir is set we should either
 *      a. be owner of dir, or
 *      b. be owner of victim, or
 *      c. have CAP_FOWNER capability
 *  6. If the victim is append-only or immutable we can't do antyhing with
 *     links pointing to it.
 *  7. If we were asked to remove a directory and victim isn't one - ENOTDIR.
 *  8. If we were asked to remove a non-directory and victim isn't one - EISDIR.
 *  9. We can't remove a root or mountpoint.
 */
static inline int may_delete(struct inode *dir,struct dentry *victim, int isdir)
{
        int error;
        if (!victim->d_inode || victim->d_parent->d_inode != dir)
                return -ENOENT;
        error = permission(dir,MAY_WRITE | MAY_EXEC);
        if (error)
                return error;
        if (IS_APPEND(dir))
                return -EPERM;
        if (check_sticky(dir, victim->d_inode)||IS_APPEND(victim->d_inode)||
            IS_IMMUTABLE(victim->d_inode))
                return -EPERM;
        if (isdir) {
                if (!S_ISDIR(victim->d_inode->i_mode))
                        return -ENOTDIR;
                if (IS_ROOT(victim))
                        return -EBUSY;
                if (victim->d_mounts != victim->d_covers)
                        return -EBUSY;
        } else if (S_ISDIR(victim->d_inode->i_mode))
                return -EISDIR;
        return 0;
}

/*      Check whether we can create an object with dentry child in directory
 *  dir.
 *  1. We can't do it if child already exists (open has special treatment for
 *     this case, but since we are inlined it's OK)
 *  2. We can't do it if dir is read-only (done in permission())
 *  3. We should have write and exec permissions on dir
 *  4. We can't do it if dir is immutable (done in permission())
 */
static inline int may_create(struct inode *dir, struct dentry *child) {
        if (child->d_inode)
                return -EEXIST;
        return permission(dir,MAY_WRITE | MAY_EXEC);
}

/* 
 * Special case: O_CREAT|O_EXCL implies O_NOFOLLOW for security
 * reasons.
 *
 * O_DIRECTORY translates into forcing a directory lookup.
 */
static inline int lookup_flags(unsigned int f)
{
        unsigned long retval = LOOKUP_FOLLOW;

        if (f & O_NOFOLLOW)
                retval &= ~LOOKUP_FOLLOW;
        
        if ((f & (O_CREAT|O_EXCL)) == (O_CREAT|O_EXCL))
                retval &= ~LOOKUP_FOLLOW;
        
        if (f & O_DIRECTORY)
                retval |= LOOKUP_DIRECTORY;
        
        return retval;
}

int vfs_create(struct inode *dir, struct dentry *dentry, int mode)
{
        int error;

        error = may_create(dir, dentry);
        if (error)
                goto exit_lock;

        error = -EACCES;        /* shouldn't it be ENOSYS? */
        if (!dir->i_op || !dir->i_op->create)
                goto exit_lock;

        DQUOT_INIT(dir);
        error = dir->i_op->create(dir, dentry, mode);
exit_lock:
        return error;
}

/*
 *      open_namei()
 *
 * namei for open - this is in fact almost the whole open-routine.
 *
 * Note that the low bits of "flag" aren't the same as in the open
 * system call - they are 00 - no permissions needed
 *                        01 - read permission needed
 *                        10 - write permission needed
 *                        11 - read/write permissions needed
 * which is a lot more logical, and also allows the "no perm" needed
 * for symlinks (where the permissions are checked later).
 */
struct dentry * open_namei(const char * pathname, int flag, int mode)
{
        int acc_mode, error;
        struct inode *inode;
        struct dentry *dentry;

        mode &= S_IALLUGO & ~current->fs->umask;
        mode |= S_IFREG;

        dentry = lookup_dentry(pathname, NULL, lookup_flags(flag));
        if (IS_ERR(dentry))
                return dentry;

        acc_mode = ACC_MODE(flag);
        if (flag & O_CREAT) {
                struct dentry *dir;

                if (dentry->d_inode) {
                        if (!(flag & O_EXCL))
                                goto nocreate;
                        error = -EEXIST;
                        goto exit;
                }

                dir = lock_parent(dentry);
                if (!check_parent(dir, dentry)) {
                        /*
                         * Really nasty race happened. What's the 
                         * right error code? We had a dentry, but
                         * before we could use it it was removed
                         * by somebody else. We could just re-try
                         * everything, I guess.
                         *
                         * ENOENT is definitely wrong.
                         */
                        error = -ENOENT;
                        unlock_dir(dir);
                        goto exit;
                }

                /*
                 * Somebody might have created the file while we
                 * waited for the directory lock.. So we have to
                 * re-do the existence test.
                 */
                if (dentry->d_inode) {
                        error = 0;
                        if (flag & O_EXCL)
                                error = -EEXIST;
                } else {
                        error = vfs_create(dir->d_inode, dentry,mode);
                        /* Don't check for write permission, don't truncate */
                        acc_mode = 0;
                        flag &= ~O_TRUNC;
                }
                unlock_dir(dir);
                if (error)
                        goto exit;
        }

nocreate:
        error = -ENOENT;
        inode = dentry->d_inode;
        if (!inode)
                goto exit;

        error = -ELOOP;
        if (S_ISLNK(inode->i_mode))
                goto exit;
        
        error = -EISDIR;
        if (S_ISDIR(inode->i_mode) && (flag & FMODE_WRITE))
                goto exit;

        error = permission(inode,acc_mode);
        if (error)
                goto exit;

        /*
         * FIFO's, sockets and device files are special: they don't
         * actually live on the filesystem itself, and as such you
         * can write to them even if the filesystem is read-only.
         */
        if (S_ISFIFO(inode->i_mode) || S_ISSOCK(inode->i_mode)) {
                flag &= ~O_TRUNC;
        } else if (S_ISBLK(inode->i_mode) || S_ISCHR(inode->i_mode)) {
                error = -EACCES;
                if (IS_NODEV(inode))
                        goto exit;

                flag &= ~O_TRUNC;
        } else {
                error = -EROFS;
                if (IS_RDONLY(inode) && (flag & 2))
                        goto exit;
        }
        /*
         * An append-only file must be opened in append mode for writing.
         */
        error = -EPERM;
        if (IS_APPEND(inode)) {
                if  ((flag & FMODE_WRITE) && !(flag & O_APPEND))
                        goto exit;
                if (flag & O_TRUNC)
                        goto exit;
        }

        if (flag & O_TRUNC) {
                error = get_write_access(inode);
                if (error)
                        goto exit;

                /*
                 * Refuse to truncate files with mandatory locks held on them.
                 */
                error = locks_verify_locked(inode);
                if (!error) {
                        DQUOT_INIT(inode);
                        
                        error = do_truncate(dentry, 0);
                }
                put_write_access(inode);
                if (error)
                        goto exit;
        } else
                if (flag & FMODE_WRITE)
                        DQUOT_INIT(inode);

        return dentry;

exit:
        dput(dentry);
        return ERR_PTR(error);
}

struct dentry * do_mknod(const char * filename, int mode, dev_t dev)
{
        int error;
        struct dentry *dir;
        struct dentry *dentry, *retval;

        mode &= ~current->fs->umask;
        dentry = lookup_dentry(filename, NULL, LOOKUP_FOLLOW);
        if (IS_ERR(dentry))
                return dentry;

        dir = lock_parent(dentry);
        error = -ENOENT;
        if (!check_parent(dir, dentry))
                goto exit_lock;

        error = may_create(dir->d_inode, dentry);
        if (error)
                goto exit_lock;

        error = -EPERM;
        if (!dir->d_inode->i_op || !dir->d_inode->i_op->mknod)
                goto exit_lock;

        DQUOT_INIT(dir->d_inode);
        error = dir->d_inode->i_op->mknod(dir->d_inode, dentry, mode, dev);
exit_lock:
        retval = ERR_PTR(error);
        if (!error)
                retval = dget(dentry);
        unlock_dir(dir);
        dput(dentry);
        return retval;
}

asmlinkage long sys_mknod(const char * filename, int mode, dev_t dev)
{
        int error;
        char * tmp;
        struct dentry * dentry;

        if (S_ISDIR(mode) || (!S_ISFIFO(mode) && !capable(CAP_MKNOD)))
                return -EPERM;
        tmp = getname(filename);
        if (IS_ERR(tmp))
                return PTR_ERR(tmp);

        error = -EINVAL;
        lock_kernel();
        switch (mode & S_IFMT) {
        case 0:
                mode |= S_IFREG;        /* fallthrough */
        case S_IFREG:
                mode &= ~current->fs->umask;
                dentry = lookup_dentry(filename, NULL, LOOKUP_FOLLOW);
                if (IS_ERR(dentry))
                        error = PTR_ERR(dentry);
                else {
                        struct dentry *dir = lock_parent(dentry);
                        error = -ENOENT;
                        if (check_parent(dir, dentry))
                                error = vfs_create(dir->d_inode, dentry, mode);
                        dput(dentry);
                }
                break;
        case S_IFCHR: case S_IFBLK: case S_IFIFO: case S_IFSOCK:
                dentry = do_mknod(tmp,mode,dev);
                error = PTR_ERR(dentry);
                if (!IS_ERR(dentry)) {
                        dput(dentry);
                        error = 0;
                }
                break;
        }
        unlock_kernel();
        putname(tmp);

        return error;
}

static inline int do_mkdir(const char * pathname, int mode)
{
        int error;
        struct dentry *dir;
        struct dentry *dentry;

        dentry = lookup_dentry(pathname, NULL, LOOKUP_SLASHOK);
        error = PTR_ERR(dentry);
        if (IS_ERR(dentry))
                goto exit;

        /*
         * EEXIST is kind of a strange error code to
         * return, but basically if the dentry was moved
         * or unlinked while we locked the parent, we
         * do know that it _did_ exist before, and as
         * such it makes perfect sense.. In contrast,
         * ENOENT doesn't make sense for mkdir.
         */
        dir = lock_parent(dentry);
        error = -EEXIST;
        if (!check_parent(dir, dentry))
                goto exit_lock;

        error = may_create(dir->d_inode, dentry);
        if (error)
                goto exit_lock;

        error = -EPERM;
        if (!dir->d_inode->i_op || !dir->d_inode->i_op->mkdir)
                goto exit_lock;

        DQUOT_INIT(dir->d_inode);
        mode &= (S_IRWXUGO|S_ISVTX) & ~current->fs->umask;
        error = dir->d_inode->i_op->mkdir(dir->d_inode, dentry, mode);

exit_lock:
        unlock_dir(dir);
        dput(dentry);
exit:
        return error;
}

asmlinkage long sys_mkdir(const char * pathname, int mode)
{
        int error;
        char * tmp;

        tmp = getname(pathname);
        if(IS_ERR(tmp))
                return PTR_ERR(tmp);
        lock_kernel();
        error = do_mkdir(tmp,mode);
        unlock_kernel();
        putname(tmp);

        return error;
}

int vfs_rmdir(struct inode *dir, struct dentry *dentry)
{
        int error;

        error = may_delete(dir, dentry, 1);
        if (error)
                return error;

        if (!dir->i_op || !dir->i_op->rmdir)
                return -EPERM;

        DQUOT_INIT(dir);

        /*
         * We try to drop the dentry early: we should have
         * a usage count of 2 if we're the only user of this
         * dentry, and if that is true (possibly after pruning
         * the dcache), then we drop the dentry now.
         *
         * A low-level filesystem can, if it choses, legally
         * do a
         *
         *      if (!list_empty(&dentry->d_hash))
         *              return -EBUSY;
         *
         * if it cannot handle the case of removing a directory
         * that is still in use by something else..
         */
        switch (dentry->d_count) {
        default:
                shrink_dcache_parent(dentry);
                if (dentry->d_count != 2)
                        break;
        case 2:
                d_drop(dentry);
        }

        error = dir->i_op->rmdir(dir, dentry);

        return error;
}

static inline int do_rmdir(const char * name)
{
        int error;
        struct dentry *dir;
        struct dentry *dentry;

        dentry = lookup_dentry(name, NULL, 0);
        error = PTR_ERR(dentry);
        if (IS_ERR(dentry))
                goto exit;

        error = -ENOENT;
        if (!dentry->d_inode)
                goto exit_dput;

        dir = dget(dentry->d_parent);

        /*
         * The dentry->d_count stuff confuses d_delete() enough to
         * not kill the inode from under us while it is locked. This
         * wouldn't be needed, except the dentry semaphore is really
         * in the inode, not in the dentry..
         */
        dentry->d_count++;
        double_lock(dir, dentry);

        error = -ENOENT;
        if (check_parent(dir, dentry))
                error = vfs_rmdir(dir->d_inode, dentry);

        double_unlock(dentry, dir);
exit_dput:
        dput(dentry);
exit:
        return error;
}

asmlinkage long sys_rmdir(const char * pathname)
{
        int error;
        char * tmp;

        tmp = getname(pathname);
        if(IS_ERR(tmp))
                return PTR_ERR(tmp);
        lock_kernel();
        error = do_rmdir(tmp);
        unlock_kernel();

        putname(tmp);

        return error;
}

int vfs_unlink(struct inode *dir, struct dentry *dentry)
{
        int error;

        error = may_delete(dir, dentry, 0);
        if (!error) {
                error = -EPERM;
                if (dir->i_op && dir->i_op->unlink) {
                        DQUOT_INIT(dir);
                        error = dir->i_op->unlink(dir, dentry);
                }
        }
        return error;
}

static inline int do_unlink(const char * name)
{
        int error;
        struct dentry *dir;
        struct dentry *dentry;

        dentry = lookup_dentry(name, NULL, 0);
        error = PTR_ERR(dentry);
        if (IS_ERR(dentry))
                goto exit;

        dir = lock_parent(dentry);
        error = -ENOENT;
        if (check_parent(dir, dentry))
                error = vfs_unlink(dir->d_inode, dentry);

        unlock_dir(dir);
        dput(dentry);
exit:
        return error;
}

asmlinkage long sys_unlink(const char * pathname)
{
        int error;
        char * tmp;

        tmp = getname(pathname);
        if(IS_ERR(tmp))
                return PTR_ERR(tmp);
        lock_kernel();
        error = do_unlink(tmp);
        unlock_kernel();
        putname(tmp);

        return error;
}

static inline int do_symlink(const char * oldname, const char * newname)
{
        int error;
        struct dentry *dir;
        struct dentry *dentry;

        dentry = lookup_dentry(newname, NULL, 0);

        error = PTR_ERR(dentry);
        if (IS_ERR(dentry))
                goto exit;

        dir = lock_parent(dentry);
        error = -ENOENT;
        if (!check_parent(dir, dentry))
                goto exit_lock;

        error = may_create(dir->d_inode, dentry);
        if (error)
                goto exit_lock;

        error = -EPERM;
        if (!dir->d_inode->i_op || !dir->d_inode->i_op->symlink)
                goto exit_lock;

        DQUOT_INIT(dir->d_inode);
        error = dir->d_inode->i_op->symlink(dir->d_inode, dentry, oldname);

exit_lock:
        unlock_dir(dir);
        dput(dentry);
exit:
        return error;
}

asmlinkage long sys_symlink(const char * oldname, const char * newname)
{
        int error;
        char * from;
        char * to;

        from = getname(oldname);
        if(IS_ERR(from))
                return PTR_ERR(from);
        to = getname(newname);
        error = PTR_ERR(to);
        if (!IS_ERR(to)) {
                lock_kernel();
                error = do_symlink(from,to);
                unlock_kernel();
                putname(to);
        }
        putname(from);
        return error;
}

static inline int do_link(const char * oldname, const char * newname)
{
        struct dentry *old_dentry, *new_dentry, *dir;
        struct inode *inode;
        int error;

        /*
         * Hardlinks are often used in delicate situations.  We avoid
         * security-related surprises by not following symlinks on the
         * newname.  --KAB
         *
         * We don't follow them on the oldname either to be compatible
         * with linux 2.0, and to avoid hard-linking to directories
         * and other special files.  --ADM
         */
        old_dentry = lookup_dentry(oldname, NULL, 0);
        error = PTR_ERR(old_dentry);
        if (IS_ERR(old_dentry))
                goto exit;

        new_dentry = lookup_dentry(newname, NULL, 0);
        error = PTR_ERR(new_dentry);
        if (IS_ERR(new_dentry))
                goto exit_old;

        dir = lock_parent(new_dentry);
        error = -ENOENT;
        if (!check_parent(dir, new_dentry))
                goto exit_lock;

        error = -ENOENT;
        inode = old_dentry->d_inode;
        if (!inode)
                goto exit_lock;

        error = may_create(dir->d_inode, new_dentry);
        if (error)
                goto exit_lock;

        error = -EXDEV;
        if (dir->d_inode->i_dev != inode->i_dev)
                goto exit_lock;

        /*
         * A link to an append-only or immutable file cannot be created.
         */
        error = -EPERM;
        if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
                goto exit_lock;

        error = -EPERM;
        if (!dir->d_inode->i_op || !dir->d_inode->i_op->link)
                goto exit_lock;

        DQUOT_INIT(dir->d_inode);
        error = dir->d_inode->i_op->link(old_dentry, dir->d_inode, new_dentry);

exit_lock:
        unlock_dir(dir);
        dput(new_dentry);
exit_old:
        dput(old_dentry);
exit:
        return error;
}

asmlinkage long sys_link(const char * oldname, const char * newname)
{
        int error;
        char * from;
                char * to;

        from = getname(oldname);
        if(IS_ERR(from))
                return PTR_ERR(from);
        to = getname(newname);
        error = PTR_ERR(to);
        if (!IS_ERR(to)) {
                lock_kernel();
                error = do_link(from,to);
                unlock_kernel();
                putname(to);
        }
        putname(from);

        return error;
}

int vfs_rename_dir(struct inode *old_dir, struct dentry *old_dentry,
               struct inode *new_dir, struct dentry *new_dentry)
{
        int error;
        int need_rehash = 0;

        if (old_dentry->d_inode == new_dentry->d_inode)
                return 0;

        error = may_delete(old_dir, old_dentry, 1);
        if (error)
                return error;

        if (new_dir->i_dev != old_dir->i_dev)
                return -EXDEV;

        if (!new_dentry->d_inode)
                error = may_create(new_dir, new_dentry);
        else
                error = may_delete(new_dir, new_dentry, 1);
        if (error)
                return error;

        if (!old_dir->i_op || !old_dir->i_op->rename)
                return -EPERM;

        /*
         * If we are going to change the parent - check write permissions,
         * we'll need to flip '..'.
         */
        if (new_dir != old_dir) {
                error = permission(old_dentry->d_inode, MAY_WRITE);
        }
        if (error)
                return error;

        DQUOT_INIT(old_dir);
        DQUOT_INIT(new_dir);
        down(&old_dir->i_sb->s_vfs_rename_sem);
        error = -EINVAL;
        if (is_subdir(new_dentry, old_dentry))
                goto out_unlock;
        if (new_dentry->d_inode) {
                error = -EBUSY;
                if (d_invalidate(new_dentry)<0)
                        goto out_unlock;
                need_rehash = 1;
        }
        error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry);
        if (need_rehash)
                d_rehash(new_dentry);
        if (!error)
                d_move(old_dentry,new_dentry);
out_unlock:
        up(&old_dir->i_sb->s_vfs_rename_sem);
        return error;
}

int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
               struct inode *new_dir, struct dentry *new_dentry)
{
        int error;

        if (old_dentry->d_inode == new_dentry->d_inode)
                return 0;

        error = may_delete(old_dir, old_dentry, 0);
        if (error)
                return error;

        if (new_dir->i_dev != old_dir->i_dev)
                return -EXDEV;

        if (!new_dentry->d_inode)
                error = may_create(new_dir, new_dentry);
        else
                error = may_delete(new_dir, new_dentry, 0);
        if (error)
                return error;

        if (!old_dir->i_op || !old_dir->i_op->rename)
                return -EPERM;

        DQUOT_INIT(old_dir);
        DQUOT_INIT(new_dir);
        error = old_dir->i_op->rename(old_dir, old_dentry, new_dir, new_dentry);
        if (error)
                return error;
        /* The following d_move() should become unconditional */
        if (!(old_dir->i_sb->s_flags & MS_ODD_RENAME)) {
                d_move(old_dentry, new_dentry);
        }
        return 0;
}

int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
               struct inode *new_dir, struct dentry *new_dentry)
{
        if (S_ISDIR(old_dentry->d_inode->i_mode))
                return vfs_rename_dir(old_dir,old_dentry,new_dir,new_dentry);
        else
                return vfs_rename_other(old_dir,old_dentry,new_dir,new_dentry);
}

static inline int do_rename(const char * oldname, const char * newname)
{
        int error;
        struct dentry * old_dir, * new_dir;
        struct dentry * old_dentry, *new_dentry;

        old_dentry = lookup_dentry(oldname, NULL, 0);

        error = PTR_ERR(old_dentry);
        if (IS_ERR(old_dentry))
                goto exit;

        error = -ENOENT;
        if (!old_dentry->d_inode)
                goto exit_old;

        {
                unsigned int flags = 0;
                if (S_ISDIR(old_dentry->d_inode->i_mode))
                        flags = LOOKUP_SLASHOK;
                new_dentry = lookup_dentry(newname, NULL, flags);
        }

        error = PTR_ERR(new_dentry);
        if (IS_ERR(new_dentry))
                goto exit_old;

        new_dir = get_parent(new_dentry);
        old_dir = get_parent(old_dentry);

        double_lock(new_dir, old_dir);

        error = -ENOENT;
        if (check_parent(old_dir, old_dentry) && check_parent(new_dir, new_dentry))
                error = vfs_rename(old_dir->d_inode, old_dentry,
                                   new_dir->d_inode, new_dentry);

        double_unlock(new_dir, old_dir);
        dput(new_dentry);
exit_old:
        dput(old_dentry);
exit:
        return error;
}

asmlinkage long sys_rename(const char * oldname, const char * newname)
{
        int error;
        char * from;
        char * to;

        from = getname(oldname);
        if(IS_ERR(from))
                return PTR_ERR(from);
        to = getname(newname);
        error = PTR_ERR(to);
        if (!IS_ERR(to)) {
                lock_kernel();
                error = do_rename(from,to);
                unlock_kernel();
                putname(to);
        }
        putname(from);
        return error;
}

int vfs_readlink(struct dentry *dentry, char *buffer, int buflen, const char *link)
{
        u32 len;

        len = PTR_ERR(link);
        if (IS_ERR(link))
                goto out;

        len = strlen(link);
        if (len > buflen)
                len = buflen;
        copy_to_user(buffer, link, len);
out:
        return len;
}

static inline struct dentry *
__vfs_follow_link(struct dentry *dentry, struct dentry *base,
                unsigned follow, const char *link)
{
        struct dentry *result;
        UPDATE_ATIME(dentry->d_inode);

        if (IS_ERR(link))
                goto fail;

        result = lookup_dentry(link, base, follow);
        return result;

fail:
        dput(base);
        return (struct dentry *)link;
}

struct dentry *
vfs_follow_link(struct dentry *dentry, struct dentry *base,
unsigned int follow, const char *link)
{
        return __vfs_follow_link(dentry,base,follow,link);
}

/* get the link contents into pagecache */
static char *page_getlink(struct dentry * dentry, struct page **ppage)
{
        struct page * page;
        struct address_space *mapping = dentry->d_inode->i_mapping;
        page = read_cache_page(mapping, 0, (filler_t *)mapping->a_ops->readpage,
                                dentry);
        if (IS_ERR(page))
                goto sync_fail;
        wait_on_page(page);
        if (!Page_Uptodate(page))
                goto async_fail;
        *ppage = page;
        return (char*) kmap(page);

async_fail:
        page_cache_release(page);
        return ERR_PTR(-EIO);

sync_fail:
        return (char*)page;
}

int page_readlink(struct dentry *dentry, char *buffer, int buflen)
{
        struct page *page = NULL;
        char *s = page_getlink(dentry, &page);
        int res = vfs_readlink(dentry,buffer,buflen,s);
        if (page) {
                kunmap(page);
                page_cache_release(page);
        }
        return res;
}

struct dentry *
page_follow_link(struct dentry *dentry, struct dentry *base, unsigned int follow)
{
        struct page *page = NULL;
        char *s = page_getlink(dentry, &page);
        struct dentry *res = __vfs_follow_link(dentry,base,follow,s);
        if (page) {
                kunmap(page);
                page_cache_release(page);
        }
        return res;
}

struct inode_operations page_symlink_inode_operations = {
        readlink:       page_readlink,
        follow_link:    page_follow_link,
};