[PATCH] uml: add host AIO support to block driver

[linux-2.6/sactl.git] / arch / um / drivers / ubd_kern.c

/* 
 * Copyright (C) 2000 Jeff Dike (jdike@karaya.com)
 * Licensed under the GPL
 */

/* 2001-09-28...2002-04-17
 * Partition stuff by James_McMechan@hotmail.com
 * old style ubd by setting UBD_SHIFT to 0
 * 2002-09-27...2002-10-18 massive tinkering for 2.5
 * partitions have changed in 2.5
 * 2003-01-29 more tinkering for 2.5.59-1
 * This should now address the sysfs problems and has
 * the symlink for devfs to allow for booting with
 * the common /dev/ubd/discX/... names rather than
 * only /dev/ubdN/discN this version also has lots of
 * clean ups preparing for ubd-many.
 * James McMechan
 */

#define MAJOR_NR UBD_MAJOR
#define UBD_SHIFT 4

#include "linux/config.h"
#include "linux/module.h"
#include "linux/blkdev.h"
#include "linux/hdreg.h"
#include "linux/init.h"
#include "linux/devfs_fs_kernel.h"
#include "linux/cdrom.h"
#include "linux/proc_fs.h"
#include "linux/ctype.h"
#include "linux/capability.h"
#include "linux/mm.h"
#include "linux/vmalloc.h"
#include "linux/blkpg.h"
#include "linux/genhd.h"
#include "linux/spinlock.h"
#include "asm/atomic.h"
#include "asm/segment.h"
#include "asm/uaccess.h"
#include "asm/irq.h"
#include "asm/types.h"
#include "asm/tlbflush.h"
#include "user_util.h"
#include "mem_user.h"
#include "kern_util.h"
#include "kern.h"
#include "mconsole_kern.h"
#include "init.h"
#include "irq_user.h"
#include "irq_kern.h"
#include "ubd_user.h"
#include "os.h"
#include "mem.h"
#include "mem_kern.h"
#include "cow.h"
#include "aio.h"

enum ubd_req { UBD_READ, UBD_WRITE };

struct io_thread_req {
        enum aio_type op;
        int fds[2];
        unsigned long offsets[2];
        unsigned long long offset;
        unsigned long length;
        char *buffer;
        int sectorsize;
        int bitmap_offset;
        long bitmap_start;
        long bitmap_end;
        int error;
};

extern int open_ubd_file(char *file, struct openflags *openflags,
                         char **backing_file_out, int *bitmap_offset_out,
                         unsigned long *bitmap_len_out, int *data_offset_out,
                         int *create_cow_out);
extern int create_cow_file(char *cow_file, char *backing_file,
                           struct openflags flags, int sectorsize,
                           int alignment, int *bitmap_offset_out,
                           unsigned long *bitmap_len_out,
                           int *data_offset_out);
extern int read_cow_bitmap(int fd, void *buf, int offset, int len);
extern void do_io(struct io_thread_req *req, struct request *r,
                  unsigned long *bitmap);

static inline int ubd_test_bit(__u64 bit, void *data)
{
        unsigned char *buffer = data;
        __u64 n;
        int bits, off;

        bits = sizeof(buffer[0]) * 8;
        n = bit / bits;
        off = bit % bits;
        return((buffer[n] & (1 << off)) != 0);
}

static inline void ubd_set_bit(__u64 bit, void *data)
{
        unsigned char *buffer = data;
        __u64 n;
        int bits, off;

        bits = sizeof(buffer[0]) * 8;
        n = bit / bits;
        off = bit % bits;
        buffer[n] |= (1 << off);
}
/*End stuff from ubd_user.h*/

#define DRIVER_NAME "uml-blkdev"

static DEFINE_SPINLOCK(ubd_io_lock);
static DEFINE_SPINLOCK(ubd_lock);

static int ubd_open(struct inode * inode, struct file * filp);
static int ubd_release(struct inode * inode, struct file * file);
static int ubd_ioctl(struct inode * inode, struct file * file,
                     unsigned int cmd, unsigned long arg);

#define MAX_DEV (8)

static struct block_device_operations ubd_blops = {
        .owner          = THIS_MODULE,
        .open           = ubd_open,
        .release        = ubd_release,
        .ioctl          = ubd_ioctl,
};

/* Protected by the queue_lock */
static request_queue_t *ubd_queue;

/* Protected by ubd_lock */
static int fake_major = MAJOR_NR;

static struct gendisk *ubd_gendisk[MAX_DEV];
static struct gendisk *fake_gendisk[MAX_DEV];
 
#ifdef CONFIG_BLK_DEV_UBD_SYNC
#define OPEN_FLAGS ((struct openflags) { .r = 1, .w = 1, .s = 1, .c = 0, \
                                         .cl = 1 })
#else
#define OPEN_FLAGS ((struct openflags) { .r = 1, .w = 1, .s = 0, .c = 0, \
                                         .cl = 1 })
#endif

/* Not protected - changed only in ubd_setup_common and then only to
 * to enable O_SYNC.
 */
static struct openflags global_openflags = OPEN_FLAGS;

struct cow {
        /* This is the backing file, actually */
        char *file;
        int fd;
        unsigned long *bitmap;
        unsigned long bitmap_len;
        int bitmap_offset;
        int data_offset;
};

#define MAX_SG 64

struct ubd {
        char *file;
        int count;
        int fd;
        __u64 size;
        struct openflags boot_openflags;
        struct openflags openflags;
        int no_cow;
        struct cow cow;
        struct platform_device pdev;
        struct scatterlist sg[MAX_SG];
};

#define DEFAULT_COW { \
        .file =                 NULL, \
        .fd =                   -1, \
        .bitmap =               NULL, \
        .bitmap_offset =        0, \
        .data_offset =          0, \
}

#define DEFAULT_UBD { \
        .file =                 NULL, \
        .count =                0, \
        .fd =                   -1, \
        .size =                 -1, \
        .boot_openflags =       OPEN_FLAGS, \
        .openflags =            OPEN_FLAGS, \
        .no_cow =               0, \
        .cow =                  DEFAULT_COW, \
}

struct ubd ubd_dev[MAX_DEV] = { [ 0 ... MAX_DEV - 1 ] = DEFAULT_UBD };

static int ubd0_init(void)
{
        struct ubd *dev = &ubd_dev[0];

        if(dev->file == NULL)
                dev->file = "root_fs";
        return(0);
}

__initcall(ubd0_init);

/* Only changed by fake_ide_setup which is a setup */
static int fake_ide = 0;
static struct proc_dir_entry *proc_ide_root = NULL;
static struct proc_dir_entry *proc_ide = NULL;

static void make_proc_ide(void)
{
        proc_ide_root = proc_mkdir("ide", NULL);
        proc_ide = proc_mkdir("ide0", proc_ide_root);
}

static int proc_ide_read_media(char *page, char **start, off_t off, int count,
                               int *eof, void *data)
{
        int len;

        strcpy(page, "disk\n");
        len = strlen("disk\n");
        len -= off;
        if (len < count){
                *eof = 1;
                if (len <= 0) return 0;
        }
        else len = count;
        *start = page + off;
        return len;
}

static void make_ide_entries(char *dev_name)
{
        struct proc_dir_entry *dir, *ent;
        char name[64];

        if(proc_ide_root == NULL) make_proc_ide();

        dir = proc_mkdir(dev_name, proc_ide);
        if(!dir) return;

        ent = create_proc_entry("media", S_IFREG|S_IRUGO, dir);
        if(!ent) return;
        ent->nlink = 1;
        ent->data = NULL;
        ent->read_proc = proc_ide_read_media;
        ent->write_proc = NULL;
        sprintf(name,"ide0/%s", dev_name);
        proc_symlink(dev_name, proc_ide_root, name);
}

static int fake_ide_setup(char *str)
{
        fake_ide = 1;
        return(1);
}

__setup("fake_ide", fake_ide_setup);

__uml_help(fake_ide_setup,
"fake_ide\n"
"    Create ide0 entries that map onto ubd devices.\n\n"
);

static int parse_unit(char **ptr)
{
        char *str = *ptr, *end;
        int n = -1;

        if(isdigit(*str)) {
                n = simple_strtoul(str, &end, 0);
                if(end == str)
                        return(-1);
                *ptr = end;
        }
        else if (('a' <= *str) && (*str <= 'h')) {
                n = *str - 'a';
                str++;
                *ptr = str;
        }
        return(n);
}

static int ubd_setup_common(char *str, int *index_out)
{
        struct ubd *dev;
        struct openflags flags = global_openflags;
        char *backing_file;
        int n, err, i;

        if(index_out) *index_out = -1;
        n = *str;
        if(n == '='){
                char *end;
                int major;

                str++;
                if(!strcmp(str, "sync")){
                        global_openflags = of_sync(global_openflags);
                        return(0);
                }
                major = simple_strtoul(str, &end, 0);
                if((*end != '\0') || (end == str)){
                        printk(KERN_ERR 
                               "ubd_setup : didn't parse major number\n");
                        return(1);
                }

                err = 1;
                spin_lock(&ubd_lock);
                if(fake_major != MAJOR_NR){
                        printk(KERN_ERR "Can't assign a fake major twice\n");
                        goto out1;
                }
 
                fake_major = major;

                printk(KERN_INFO "Setting extra ubd major number to %d\n",
                       major);
                err = 0;
        out1:
                spin_unlock(&ubd_lock);
                return(err);
        }

        n = parse_unit(&str);
        if(n < 0){
                printk(KERN_ERR "ubd_setup : couldn't parse unit number "
                       "'%s'\n", str);
                return(1);
        }
        if(n >= MAX_DEV){
                printk(KERN_ERR "ubd_setup : index %d out of range "
                       "(%d devices, from 0 to %d)\n", n, MAX_DEV, MAX_DEV - 1);
                return(1);
        }

        err = 1;
        spin_lock(&ubd_lock);

        dev = &ubd_dev[n];
        if(dev->file != NULL){
                printk(KERN_ERR "ubd_setup : device already configured\n");
                goto out;
        }

        if (index_out)
                *index_out = n;

        for (i = 0; i < 4; i++) {
                switch (*str) {
                case 'r':
                        flags.w = 0;
                        break;
                case 's':
                        flags.s = 1;
                        break;
                case 'd':
                        dev->no_cow = 1;
                        break;
                case '=':
                        str++;
                        goto break_loop;
                default:
                        printk(KERN_ERR "ubd_setup : Expected '=' or flag letter (r,s or d)\n");
                        goto out;
                }
                str++;
        }

        if (*str == '=')
                printk(KERN_ERR "ubd_setup : Too many flags specified\n");
        else
                printk(KERN_ERR "ubd_setup : Expected '='\n");
        goto out;

break_loop:
        err = 0;
        backing_file = strchr(str, ',');

        if (!backing_file) {
                backing_file = strchr(str, ':');
        }

        if(backing_file){
                if(dev->no_cow)
                        printk(KERN_ERR "Can't specify both 'd' and a "
                               "cow file\n");
                else {
                        *backing_file = '\0';
                        backing_file++;
                }
        }
        dev->file = str;
        dev->cow.file = backing_file;
        dev->boot_openflags = flags;
out:
        spin_unlock(&ubd_lock);
        return(err);
}

static int ubd_setup(char *str)
{
        ubd_setup_common(str, NULL);
        return(1);
}

__setup("ubd", ubd_setup);
__uml_help(ubd_setup,
"ubd<n><flags>=<filename>[(:|,)<filename2>]\n"
"    This is used to associate a device with a file in the underlying\n"
"    filesystem. When specifying two filenames, the first one is the\n"
"    COW name and the second is the backing file name. As separator you can\n"
"    use either a ':' or a ',': the first one allows writing things like;\n"
"       ubd0=~/Uml/root_cow:~/Uml/root_backing_file\n"
"    while with a ',' the shell would not expand the 2nd '~'.\n"
"    When using only one filename, UML will detect whether to thread it like\n"
"    a COW file or a backing file. To override this detection, add the 'd'\n"
"    flag:\n"
"       ubd0d=BackingFile\n"
"    Usually, there is a filesystem in the file, but \n"
"    that's not required. Swap devices containing swap files can be\n"
"    specified like this. Also, a file which doesn't contain a\n"
"    filesystem can have its contents read in the virtual \n"
"    machine by running 'dd' on the device. <n> must be in the range\n"
"    0 to 7. Appending an 'r' to the number will cause that device\n"
"    to be mounted read-only. For example ubd1r=./ext_fs. Appending\n"
"    an 's' will cause data to be written to disk on the host immediately.\n\n"
);

static int udb_setup(char *str)
{
        printk("udb%s specified on command line is almost certainly a ubd -> "
               "udb TYPO\n", str);
        return(1);
}

__setup("udb", udb_setup);
__uml_help(udb_setup,
"udb\n"
"    This option is here solely to catch ubd -> udb typos, which can be\n"
"    to impossible to catch visually unless you specifically look for\n"
"    them.  The only result of any option starting with 'udb' is an error\n"
"    in the boot output.\n\n"
);

static int fakehd_set = 0;
static int fakehd(char *str)
{
        printk(KERN_INFO "fakehd : Changing ubd name to \"hd\".\n");
        fakehd_set = 1;
        return 1;
}

__setup("fakehd", fakehd);
__uml_help(fakehd,
"fakehd\n"
"    Change the ubd device name to \"hd\".\n\n"
);

static void do_ubd_request(request_queue_t * q);
static int in_ubd;

/* Changed by ubd_handler, which is serialized because interrupts only
 * happen on CPU 0.
 */
int intr_count = 0;

static void ubd_end_request(struct request *req, int bytes, int uptodate)
{
        if (!end_that_request_first(req, uptodate, bytes >> 9)) {
                add_disk_randomness(req->rq_disk);
                end_that_request_last(req);
        }
}

/* call ubd_finish if you need to serialize */
static void __ubd_finish(struct request *req, int bytes)
{
        if(bytes < 0){
                ubd_end_request(req, 0, 0);
                return;
        }

        ubd_end_request(req, bytes, 1);
}

static inline void ubd_finish(struct request *req, int bytes)
{
        spin_lock(&ubd_io_lock);
        __ubd_finish(req, bytes);
        spin_unlock(&ubd_io_lock);
}

struct bitmap_io {
        atomic_t count;
        struct aio_context aio;
};

struct ubd_aio {
        struct aio_context aio;
        struct request *req;
        int len;
        struct bitmap_io *bitmap;
        void *bitmap_buf;
};

static int ubd_reply_fd = -1;

static irqreturn_t ubd_intr(int irq, void *dev, struct pt_regs *unused)
{
        struct aio_thread_reply reply;
        struct ubd_aio *aio;
        struct request *req;
        int err, n, fd = (int) (long) dev;

        while(1){
                err = os_read_file(fd, &reply, sizeof(reply));
                if(err == -EAGAIN)
                        break;
                if(err < 0){
                        printk("ubd_aio_handler - read returned err %d\n",
                               -err);
                        break;
                }

                aio = container_of(reply.data, struct ubd_aio, aio);
                n = reply.err;

                if(n == 0){
                        req = aio->req;
                        req->nr_sectors -= aio->len >> 9;

                        if((aio->bitmap != NULL) &&
                           (atomic_dec_and_test(&aio->bitmap->count))){
                                aio->aio = aio->bitmap->aio;
                                aio->len = 0;
                                kfree(aio->bitmap);
                                aio->bitmap = NULL;
                                submit_aio(&aio->aio);
                        }
                        else {
                                if((req->nr_sectors == 0) &&
                                   (aio->bitmap == NULL)){
                                        int len = req->hard_nr_sectors << 9;
                                        ubd_finish(req, len);
                                }

                                if(aio->bitmap_buf != NULL)
                                        kfree(aio->bitmap_buf);
                                kfree(aio);
                        }
                }
                else if(n < 0){
                        ubd_finish(aio->req, n);
                        if(aio->bitmap != NULL)
                                kfree(aio->bitmap);
                        if(aio->bitmap_buf != NULL)
                                kfree(aio->bitmap_buf);
                        kfree(aio);
                }
        }
        reactivate_fd(fd, UBD_IRQ);

        do_ubd_request(ubd_queue);

        return(IRQ_HANDLED);
}

static int ubd_file_size(struct ubd *dev, __u64 *size_out)
{
        char *file;

        file = dev->cow.file ? dev->cow.file : dev->file;
        return(os_file_size(file, size_out));
}

static void ubd_close(struct ubd *dev)
{
        os_close_file(dev->fd);
        if(dev->cow.file == NULL)
                return;

        os_close_file(dev->cow.fd);
        vfree(dev->cow.bitmap);
        dev->cow.bitmap = NULL;
}

static int ubd_open_dev(struct ubd *dev)
{
        struct openflags flags;
        char **back_ptr;
        int err, create_cow, *create_ptr;

        dev->openflags = dev->boot_openflags;
        create_cow = 0;
        create_ptr = (dev->cow.file != NULL) ? &create_cow : NULL;
        back_ptr = dev->no_cow ? NULL : &dev->cow.file;
        dev->fd = open_ubd_file(dev->file, &dev->openflags, back_ptr,
                                &dev->cow.bitmap_offset, &dev->cow.bitmap_len, 
                                &dev->cow.data_offset, create_ptr);

        if((dev->fd == -ENOENT) && create_cow){
                dev->fd = create_cow_file(dev->file, dev->cow.file,
                                          dev->openflags, 1 << 9, PAGE_SIZE,
                                          &dev->cow.bitmap_offset, 
                                          &dev->cow.bitmap_len,
                                          &dev->cow.data_offset);
                if(dev->fd >= 0){
                        printk(KERN_INFO "Creating \"%s\" as COW file for "
                               "\"%s\"\n", dev->file, dev->cow.file);
                }
        }

        if(dev->fd < 0){
                printk("Failed to open '%s', errno = %d\n", dev->file,
                       -dev->fd);
                return(dev->fd);
        }

        if(dev->cow.file != NULL){
                err = -ENOMEM;
                dev->cow.bitmap = (void *) vmalloc(dev->cow.bitmap_len);
                if(dev->cow.bitmap == NULL){
                        printk(KERN_ERR "Failed to vmalloc COW bitmap\n");
                        goto error;
                }
                flush_tlb_kernel_vm();

                err = read_cow_bitmap(dev->fd, dev->cow.bitmap, 
                                      dev->cow.bitmap_offset, 
                                      dev->cow.bitmap_len);
                if(err < 0)
                        goto error;

                flags = dev->openflags;
                flags.w = 0;
                err = open_ubd_file(dev->cow.file, &flags, NULL, NULL, NULL, 
                                    NULL, NULL);
                if(err < 0) goto error;
                dev->cow.fd = err;
        }
        return(0);
 error:
        os_close_file(dev->fd);
        return(err);
}

static int ubd_new_disk(int major, u64 size, int unit,
                        struct gendisk **disk_out)
                        
{
        struct gendisk *disk;
        char from[sizeof("ubd/nnnnn\0")], to[sizeof("discnnnnn/disc\0")];
        int err;

        disk = alloc_disk(1 << UBD_SHIFT);
        if(disk == NULL)
                return(-ENOMEM);

        disk->major = major;
        disk->first_minor = unit << UBD_SHIFT;
        disk->fops = &ubd_blops;
        set_capacity(disk, size / 512);
        if(major == MAJOR_NR){
                sprintf(disk->disk_name, "ubd%c", 'a' + unit);
                sprintf(disk->devfs_name, "ubd/disc%d", unit);
                sprintf(from, "ubd/%d", unit);
                sprintf(to, "disc%d/disc", unit);
                err = devfs_mk_symlink(from, to);
                if(err)
                        printk("ubd_new_disk failed to make link from %s to "
                               "%s, error = %d\n", from, to, err);
        }
        else {
                sprintf(disk->disk_name, "ubd_fake%d", unit);
                sprintf(disk->devfs_name, "ubd_fake/disc%d", unit);
        }

        /* sysfs register (not for ide fake devices) */
        if (major == MAJOR_NR) {
                ubd_dev[unit].pdev.id   = unit;
                ubd_dev[unit].pdev.name = DRIVER_NAME;
                platform_device_register(&ubd_dev[unit].pdev);
                disk->driverfs_dev = &ubd_dev[unit].pdev.dev;
        }

        disk->private_data = &ubd_dev[unit];
        disk->queue = ubd_queue;
        add_disk(disk);

        *disk_out = disk;
        return 0;
}

#define ROUND_BLOCK(n) ((n + ((1 << 9) - 1)) & (-1 << 9))

static int ubd_add(int n)
{
        struct ubd *dev = &ubd_dev[n];
        int err;

        err = -ENODEV;
        if(dev->file == NULL)
                goto out;

        if (ubd_open_dev(dev))
                goto out;

        err = ubd_file_size(dev, &dev->size);
        if(err < 0)
                goto out_close;

        dev->size = ROUND_BLOCK(dev->size);

        err = ubd_new_disk(MAJOR_NR, dev->size, n, &ubd_gendisk[n]);
        if(err) 
                goto out_close;
 
        if(fake_major != MAJOR_NR)
                ubd_new_disk(fake_major, dev->size, n, 
                             &fake_gendisk[n]);

        /* perhaps this should also be under the "if (fake_major)" above */
        /* using the fake_disk->disk_name and also the fakehd_set name */
        if (fake_ide)
                make_ide_entries(ubd_gendisk[n]->disk_name);

        err = 0;
out_close:
        ubd_close(dev);
out:
        return err;
}

static int ubd_config(char *str)
{
        int n, err;

        str = uml_strdup(str);
        if(str == NULL){
                printk(KERN_ERR "ubd_config failed to strdup string\n");
                return(1);
        }
        err = ubd_setup_common(str, &n);
        if(err){
                kfree(str);
                return(-1);
        }
        if(n == -1) return(0);

        spin_lock(&ubd_lock);
        err = ubd_add(n);
        if(err)
                ubd_dev[n].file = NULL;
        spin_unlock(&ubd_lock);

        return(err);
}

static int ubd_get_config(char *name, char *str, int size, char **error_out)
{
        struct ubd *dev;
        int n, len = 0;

        n = parse_unit(&name);
        if((n >= MAX_DEV) || (n < 0)){
                *error_out = "ubd_get_config : device number out of range";
                return(-1);
        }

        dev = &ubd_dev[n];
        spin_lock(&ubd_lock);

        if(dev->file == NULL){
                CONFIG_CHUNK(str, size, len, "", 1);
                goto out;
        }

        CONFIG_CHUNK(str, size, len, dev->file, 0);

        if(dev->cow.file != NULL){
                CONFIG_CHUNK(str, size, len, ",", 0);
                CONFIG_CHUNK(str, size, len, dev->cow.file, 1);
        }
        else CONFIG_CHUNK(str, size, len, "", 1);

 out:
        spin_unlock(&ubd_lock);
        return(len);
}

static int ubd_id(char **str, int *start_out, int *end_out)
{
        int n;

        n = parse_unit(str);
        *start_out = 0;
        *end_out = MAX_DEV - 1;
        return n;
}

static int ubd_remove(int n)
{
        struct ubd *dev;
        int err = -ENODEV;

        spin_lock(&ubd_lock);

        if(ubd_gendisk[n] == NULL)
                goto out;

        dev = &ubd_dev[n];

        if(dev->file == NULL)
                goto out;

        /* you cannot remove a open disk */
        err = -EBUSY;
        if(dev->count > 0)
                goto out;

        del_gendisk(ubd_gendisk[n]);
        put_disk(ubd_gendisk[n]);
        ubd_gendisk[n] = NULL;

        if(fake_gendisk[n] != NULL){
                del_gendisk(fake_gendisk[n]);
                put_disk(fake_gendisk[n]);
                fake_gendisk[n] = NULL;
        }

        platform_device_unregister(&dev->pdev);
        *dev = ((struct ubd) DEFAULT_UBD);
        err = 0;
out:
        spin_unlock(&ubd_lock);
        return err;
}

static struct mc_device ubd_mc = {
        .name           = "ubd",
        .config         = ubd_config,
        .get_config     = ubd_get_config,
        .id             = ubd_id,
        .remove         = ubd_remove,
};

static int ubd_mc_init(void)
{
        mconsole_register_dev(&ubd_mc);
        return 0;
}

__initcall(ubd_mc_init);

static struct device_driver ubd_driver = {
        .name  = DRIVER_NAME,
        .bus   = &platform_bus_type,
};

int ubd_init(void)
{
        int i;

        ubd_reply_fd = init_aio_irq(UBD_IRQ, "ubd", ubd_intr);
        if(ubd_reply_fd < 0)
                printk("Setting up ubd AIO failed, err = %d\n", ubd_reply_fd);

        devfs_mk_dir("ubd");
        if (register_blkdev(MAJOR_NR, "ubd"))
                return -1;

        ubd_queue = blk_init_queue(do_ubd_request, &ubd_io_lock);
        if (!ubd_queue) {
                unregister_blkdev(MAJOR_NR, "ubd");
                return -1;
        }
                
        blk_queue_max_hw_segments(ubd_queue, MAX_SG);
        if (fake_major != MAJOR_NR) {
                char name[sizeof("ubd_nnn\0")];

                snprintf(name, sizeof(name), "ubd_%d", fake_major);
                devfs_mk_dir(name);
                if (register_blkdev(fake_major, "ubd"))
                        return -1;
        }
        driver_register(&ubd_driver);
        for (i = 0; i < MAX_DEV; i++) 
                ubd_add(i);

        return 0;
}

late_initcall(ubd_init);

static int ubd_open(struct inode *inode, struct file *filp)
{
        struct gendisk *disk = inode->i_bdev->bd_disk;
        struct ubd *dev = disk->private_data;
        int err = 0;

        if(dev->count == 0){
                err = ubd_open_dev(dev);
                if(err){
                        printk(KERN_ERR "%s: Can't open \"%s\": errno = %d\n",
                               disk->disk_name, dev->file, -err);
                        goto out;
                }
        }
        dev->count++;
        set_disk_ro(disk, !dev->openflags.w);

        /* This should no more be needed. And it didn't work anyway to exclude
         * read-write remounting of filesystems.*/
        /*if((filp->f_mode & FMODE_WRITE) && !dev->openflags.w){
                if(--dev->count == 0) ubd_close(dev);
                err = -EROFS;
        }*/
 out:
        return(err);
}

static int ubd_release(struct inode * inode, struct file * file)
{
        struct gendisk *disk = inode->i_bdev->bd_disk;
        struct ubd *dev = disk->private_data;

        if(--dev->count == 0)
                ubd_close(dev);
        return(0);
}

static void cowify_bitmap(struct io_thread_req *req, unsigned long *bitmap)
{
        __u64 sector = req->offset / req->sectorsize;
        int i;

        for(i = 0; i < req->length / req->sectorsize; i++){
                if(ubd_test_bit(sector + i, bitmap))
                        continue;

                if(req->bitmap_start == -1)
                        req->bitmap_start = sector + i;
                req->bitmap_end = sector + i + 1;

                ubd_set_bit(sector + i, bitmap);
        }
}

/* Called with ubd_io_lock held */
static int prepare_request(struct request *req, struct io_thread_req *io_req,
                           unsigned long long offset, int page_offset,
                           int len, struct page *page)
{
        struct gendisk *disk = req->rq_disk;
        struct ubd *dev = disk->private_data;

        /* This should be impossible now */
        if((rq_data_dir(req) == WRITE) && !dev->openflags.w){
                printk("Write attempted on readonly ubd device %s\n", 
                       disk->disk_name);
                ubd_end_request(req, 0, 0);
                return(1);
        }

        io_req->fds[0] = (dev->cow.file != NULL) ? dev->cow.fd : dev->fd;
        io_req->fds[1] = dev->fd;
        io_req->offset = offset;
        io_req->length = len;
        io_req->error = 0;
        io_req->op = (rq_data_dir(req) == READ) ? AIO_READ : AIO_WRITE;
        io_req->offsets[0] = 0;
        io_req->offsets[1] = dev->cow.data_offset;
        io_req->buffer = page_address(page) + page_offset;
        io_req->sectorsize = 1 << 9;
        io_req->bitmap_offset = dev->cow.bitmap_offset;
        io_req->bitmap_start = -1;
        io_req->bitmap_end = -1;

        if((dev->cow.file != NULL) && (io_req->op == UBD_WRITE))
                cowify_bitmap(io_req, dev->cow.bitmap);
        return(0);
}

/* Called with ubd_io_lock held */
static void do_ubd_request(request_queue_t *q)
{
        struct io_thread_req io_req;
        struct request *req;
        __u64 sector;
        int err;

        if(in_ubd)
                return;
        in_ubd = 1;
        while((req = elv_next_request(q)) != NULL){
                struct gendisk *disk = req->rq_disk;
                struct ubd *dev = disk->private_data;
                int n, i;

                blkdev_dequeue_request(req);

                sector = req->sector;
                n = blk_rq_map_sg(q, req, dev->sg);

                for(i = 0; i < n; i++){
                        struct scatterlist *sg = &dev->sg[i];

                        err = prepare_request(req, &io_req, sector << 9,
                                              sg->offset, sg->length,
                                              sg->page);
                        if(err)
                                continue;

                        sector += sg->length >> 9;
                        do_io(&io_req, req, dev->cow.bitmap);
                }
        }
        in_ubd = 0;
}

static int ubd_ioctl(struct inode * inode, struct file * file,
                     unsigned int cmd, unsigned long arg)
{
        struct hd_geometry __user *loc = (struct hd_geometry __user *) arg;
        struct ubd *dev = inode->i_bdev->bd_disk->private_data;
        struct hd_driveid ubd_id = {
                .cyls           = 0,
                .heads          = 128,
                .sectors        = 32,
        };

        switch (cmd) {
                struct hd_geometry g;
                struct cdrom_volctrl volume;
        case HDIO_GETGEO:
                if(!loc) return(-EINVAL);
                g.heads = 128;
                g.sectors = 32;
                g.cylinders = dev->size / (128 * 32 * 512);
                g.start = get_start_sect(inode->i_bdev);
                return(copy_to_user(loc, &g, sizeof(g)) ? -EFAULT : 0);

        case HDIO_GET_IDENTITY:
                ubd_id.cyls = dev->size / (128 * 32 * 512);
                if(copy_to_user((char __user *) arg, (char *) &ubd_id,
                                 sizeof(ubd_id)))
                        return(-EFAULT);
                return(0);
                
        case CDROMVOLREAD:
                if(copy_from_user(&volume, (char __user *) arg, sizeof(volume)))
                        return(-EFAULT);
                volume.channel0 = 255;
                volume.channel1 = 255;
                volume.channel2 = 255;
                volume.channel3 = 255;
                if(copy_to_user((char __user *) arg, &volume, sizeof(volume)))
                        return(-EFAULT);
                return(0);
        }
        return(-EINVAL);
}

static int same_backing_files(char *from_cmdline, char *from_cow, char *cow)
{
        struct uml_stat buf1, buf2;
        int err;

        if(from_cmdline == NULL) return(1);
        if(!strcmp(from_cmdline, from_cow)) return(1);

        err = os_stat_file(from_cmdline, &buf1);
        if(err < 0){
                printk("Couldn't stat '%s', err = %d\n", from_cmdline, -err);
                return(1);
        }
        err = os_stat_file(from_cow, &buf2);
        if(err < 0){
                printk("Couldn't stat '%s', err = %d\n", from_cow, -err);
                return(1);
        }
        if((buf1.ust_dev == buf2.ust_dev) && (buf1.ust_ino == buf2.ust_ino))
                return(1);

        printk("Backing file mismatch - \"%s\" requested,\n"
               "\"%s\" specified in COW header of \"%s\"\n",
               from_cmdline, from_cow, cow);
        return(0);
}

static int backing_file_mismatch(char *file, __u64 size, time_t mtime)
{
        unsigned long modtime;
        long long actual;
        int err;

        err = os_file_modtime(file, &modtime);
        if(err < 0){
                printk("Failed to get modification time of backing file "
                       "\"%s\", err = %d\n", file, -err);
                return(err);
        }

        err = os_file_size(file, &actual);
        if(err < 0){
                printk("Failed to get size of backing file \"%s\", "
                       "err = %d\n", file, -err);
                return(err);
        }

        if(actual != size){
                /*__u64 can be a long on AMD64 and with %lu GCC complains; so
                 * the typecast.*/
                printk("Size mismatch (%llu vs %llu) of COW header vs backing "
                       "file\n", (unsigned long long) size, actual);
                return(-EINVAL);
        }
        if(modtime != mtime){
                printk("mtime mismatch (%ld vs %ld) of COW header vs backing "
                       "file\n", mtime, modtime);
                return(-EINVAL);
        }
        return(0);
}

int read_cow_bitmap(int fd, void *buf, int offset, int len)
{
        int err;

        err = os_seek_file(fd, offset);
        if(err < 0)
                return(err);

        err = os_read_file(fd, buf, len);
        if(err < 0)
                return(err);

        return(0);
}

int open_ubd_file(char *file, struct openflags *openflags,
                  char **backing_file_out, int *bitmap_offset_out,
                  unsigned long *bitmap_len_out, int *data_offset_out,
                  int *create_cow_out)
{
        time_t mtime;
        unsigned long long size;
        __u32 version, align;
        char *backing_file;
        int fd, err, sectorsize, same, mode = 0644;

        fd = os_open_file(file, *openflags, mode);
        if(fd < 0){
                if((fd == -ENOENT) && (create_cow_out != NULL))
                        *create_cow_out = 1;
                if(!openflags->w ||
                   ((fd != -EROFS) && (fd != -EACCES))) return(fd);
                openflags->w = 0;
                fd = os_open_file(file, *openflags, mode);
                if(fd < 0)
                        return(fd);
        }

        err = os_lock_file(fd, openflags->w);
        if(err < 0){
                printk("Failed to lock '%s', err = %d\n", file, -err);
                goto out_close;
        }

        if(backing_file_out == NULL) return(fd);

        err = read_cow_header(file_reader, &fd, &version, &backing_file, &mtime,
                              &size, &sectorsize, &align, bitmap_offset_out);
        if(err && (*backing_file_out != NULL)){
                printk("Failed to read COW header from COW file \"%s\", "
                       "errno = %d\n", file, -err);
                goto out_close;
        }
        if(err) return(fd);

        if(backing_file_out == NULL) return(fd);

        same = same_backing_files(*backing_file_out, backing_file, file);

        if(!same && !backing_file_mismatch(*backing_file_out, size, mtime)){
                printk("Switching backing file to '%s'\n", *backing_file_out);
                err = write_cow_header(file, fd, *backing_file_out,
                                       sectorsize, align, &size);
                if(err){
                        printk("Switch failed, errno = %d\n", -err);
                        return(err);
                }
        }
        else {
                *backing_file_out = backing_file;
                err = backing_file_mismatch(*backing_file_out, size, mtime);
                if(err) goto out_close;
        }

        cow_sizes(version, size, sectorsize, align, *bitmap_offset_out,
                  bitmap_len_out, data_offset_out);

        return(fd);
 out_close:
        os_close_file(fd);
        return(err);
}

int create_cow_file(char *cow_file, char *backing_file, struct openflags flags,
                    int sectorsize, int alignment, int *bitmap_offset_out,
                    unsigned long *bitmap_len_out, int *data_offset_out)
{
        int err, fd;

        flags.c = 1;
        fd = open_ubd_file(cow_file, &flags, NULL, NULL, NULL, NULL, NULL);
        if(fd < 0){
                err = fd;
                printk("Open of COW file '%s' failed, errno = %d\n", cow_file,
                       -err);
                goto out;
        }

        err = init_cow_file(fd, cow_file, backing_file, sectorsize, alignment,
                            bitmap_offset_out, bitmap_len_out,
                            data_offset_out);
        if(!err)
                return(fd);
        os_close_file(fd);
 out:
        return(err);
}

void do_io(struct io_thread_req *req, struct request *r, unsigned long *bitmap)
{
        struct ubd_aio *aio;
        struct bitmap_io *bitmap_io = NULL;
        char *buf;
        void *bitmap_buf = NULL;
        unsigned long len, sector;
        int nsectors, start, end, bit, err;
        __u64 off;

        if(req->bitmap_start != -1){
                /* Round up to the nearest word */
                int round = sizeof(unsigned long);
                len = (req->bitmap_end - req->bitmap_start +
                       round * 8 - 1) / (round * 8);
                len *= round;

                off = req->bitmap_start / (8 * round);
                off *= round;

                bitmap_io = kmalloc(sizeof(*bitmap_io), GFP_KERNEL);
                if(bitmap_io == NULL){
                        printk("Failed to kmalloc bitmap IO\n");
                        req->error = 1;
                        return;
                }

                bitmap_buf = kmalloc(len, GFP_KERNEL);
                if(bitmap_buf == NULL){
                        printk("do_io : kmalloc of bitmap chunk "
                               "failed\n");
                        kfree(bitmap_io);
                        req->error = 1;
                        return;
                }
                memcpy(bitmap_buf, &bitmap[off / sizeof(bitmap[0])], len);

                *bitmap_io = ((struct bitmap_io)
                        { .count        = ATOMIC_INIT(0),
                          .aio          = INIT_AIO(AIO_WRITE, req->fds[1],
                                                   bitmap_buf, len,
                                                   req->bitmap_offset + off,
                                                   ubd_reply_fd) } );
        }

        nsectors = req->length / req->sectorsize;
        start = 0;
        end = nsectors;
        bit = 0;
        do {
                if(bitmap != NULL){
                        sector = req->offset / req->sectorsize;
                        bit = ubd_test_bit(sector + start, bitmap);
                        end = start;
                        while((end < nsectors) &&
                              (ubd_test_bit(sector + end, bitmap) == bit))
                                end++;
                }

                off = req->offsets[bit] + req->offset +
                        start * req->sectorsize;
                len = (end - start) * req->sectorsize;
                buf = &req->buffer[start * req->sectorsize];

                aio = kmalloc(sizeof(*aio), GFP_KERNEL);
                if(aio == NULL){
                        req->error = 1;
                        return;
                }

                *aio = ((struct ubd_aio)
                        { .aio          = INIT_AIO(req->op, req->fds[bit], buf,
                                                   len, off, ubd_reply_fd),
                          .len          = len,
                          .req          = r,
                          .bitmap       = bitmap_io,
                          .bitmap_buf   = bitmap_buf });

                if(aio->bitmap != NULL)
                        atomic_inc(&aio->bitmap->count);

                err = submit_aio(&aio->aio);
                if(err){
                        printk("do_io - submit_aio failed, "
                               "err = %d\n", err);
                        req->error = 1;
                        return;
                }

                start = end;
        } while(start < nsectors);
}