Patch 7.0.167

[MacVim/jjgod.git] / src / memfile.c

/* vi:set ts=8 sts=4 sw=4:
 *
 * VIM - Vi IMproved    by Bram Moolenaar
 *
 * Do ":help uganda"  in Vim to read copying and usage conditions.
 * Do ":help credits" in Vim to see a list of people who contributed.
 * See README.txt for an overview of the Vim source code.
 */

/*
 * memfile.c: Contains the functions for handling blocks of memory which can
 * be stored in a file. This is the implementation of a sort of virtual memory.
 *
 * A memfile consists of a sequence of blocks. The blocks numbered from 0
 * upwards have been assigned a place in the actual file. The block number
 * is equal to the page number in the file. The
 * blocks with negative numbers are currently in memory only. They can be
 * assigned a place in the file when too much memory is being used. At that
 * moment they get a new, positive, number. A list is used for translation of
 * negative to positive numbers.
 *
 * The size of a block is a multiple of a page size, normally the page size of
 * the device the file is on. Most blocks are 1 page long. A Block of multiple
 * pages is used for a line that does not fit in a single page.
 *
 * Each block can be in memory and/or in a file. The block stays in memory
 * as long as it is locked. If it is no longer locked it can be swapped out to
 * the file. It is only written to the file if it has been changed.
 *
 * Under normal operation the file is created when opening the memory file and
 * deleted when closing the memory file. Only with recovery an existing memory
 * file is opened.
 */

#if defined MSDOS || defined(WIN32) || defined(_WIN64)
# include "vimio.h"     /* for lseek(), must be before vim.h */
#endif

#include "vim.h"

#ifdef HAVE_FCNTL_H
# include <fcntl.h>
#endif

/*
 * Some systems have the page size in statfs.f_bsize, some in stat.st_blksize
 */
#ifdef HAVE_ST_BLKSIZE
# define STATFS stat
# define F_BSIZE st_blksize
# define fstatfs(fd, buf, len, nul) mch_fstat((fd), (buf))
#else
# ifdef HAVE_SYS_STATFS_H
#  include <sys/statfs.h>
#  define STATFS statfs
#  define F_BSIZE f_bsize
#  ifdef __MINT__               /* do we still need this? */
#   define fstatfs(fd, buf, len, nul) mch_fstat((fd), (buf))
#  endif
# endif
#endif

/*
 * for Amiga Dos 2.0x we use Flush
 */
#ifdef AMIGA
# ifdef FEAT_ARP
extern int dos2;                        /* this is in os_amiga.c */
# endif
# ifdef SASC
#  include <proto/dos.h>
#  include <ios1.h>                     /* for chkufb() */
# endif
#endif

#define MEMFILE_PAGE_SIZE 4096          /* default page size */

static long_u   total_mem_used = 0;     /* total memory used for memfiles */
static int      dont_release = FALSE;   /* don't release blocks */

static void mf_ins_hash __ARGS((memfile_T *, bhdr_T *));
static void mf_rem_hash __ARGS((memfile_T *, bhdr_T *));
static bhdr_T *mf_find_hash __ARGS((memfile_T *, blocknr_T));
static void mf_ins_used __ARGS((memfile_T *, bhdr_T *));
static void mf_rem_used __ARGS((memfile_T *, bhdr_T *));
static bhdr_T *mf_release __ARGS((memfile_T *, int));
static bhdr_T *mf_alloc_bhdr __ARGS((memfile_T *, int));
static void mf_free_bhdr __ARGS((bhdr_T *));
static void mf_ins_free __ARGS((memfile_T *, bhdr_T *));
static bhdr_T *mf_rem_free __ARGS((memfile_T *));
static int  mf_read __ARGS((memfile_T *, bhdr_T *));
static int  mf_write __ARGS((memfile_T *, bhdr_T *));
static int  mf_trans_add __ARGS((memfile_T *, bhdr_T *));
static void mf_do_open __ARGS((memfile_T *, char_u *, int));

/*
 * The functions for using a memfile:
 *
 * mf_open()        open a new or existing memfile
 * mf_open_file()   open a swap file for an existing memfile
 * mf_close()       close (and delete) a memfile
 * mf_new()         create a new block in a memfile and lock it
 * mf_get()         get an existing block and lock it
 * mf_put()         unlock a block, may be marked for writing
 * mf_free()        remove a block
 * mf_sync()        sync changed parts of memfile to disk
 * mf_release_all() release as much memory as possible
 * mf_trans_del()   may translate negative to positive block number
 * mf_fullname()    make file name full path (use before first :cd)
 */

/*
 * Open an existing or new memory block file.
 *
 *  fname:      name of file to use (NULL means no file at all)
 *              Note: fname must have been allocated, it is not copied!
 *                      If opening the file fails, fname is freed.
 *  flags:      flags for open() call
 *
 *  If fname != NULL and file cannot be opened, fail.
 *
 * return value: identifier for this memory block file.
 */
    memfile_T *
mf_open(fname, flags)
    char_u      *fname;
    int         flags;
{
    memfile_T           *mfp;
    int                 i;
    off_t               size;
#if defined(STATFS) && defined(UNIX) && !defined(__QNX__)
# define USE_FSTATFS
    struct STATFS       stf;
#endif

    if ((mfp = (memfile_T *)alloc((unsigned)sizeof(memfile_T))) == NULL)
        return NULL;

    if (fname == NULL)      /* no file for this memfile, use memory only */
    {
        mfp->mf_fname = NULL;
        mfp->mf_ffname = NULL;
        mfp->mf_fd = -1;
    }
    else
    {
        mf_do_open(mfp, fname, flags);  /* try to open the file */

        /* if the file cannot be opened, return here */
        if (mfp->mf_fd < 0)
        {
            vim_free(mfp);
            return NULL;
        }
    }

    mfp->mf_free_first = NULL;          /* free list is empty */
    mfp->mf_used_first = NULL;          /* used list is empty */
    mfp->mf_used_last = NULL;
    mfp->mf_dirty = FALSE;
    mfp->mf_used_count = 0;
    for (i = 0; i < MEMHASHSIZE; ++i)
    {
        mfp->mf_hash[i] = NULL;         /* hash lists are empty */
        mfp->mf_trans[i] = NULL;        /* trans lists are empty */
    }
    mfp->mf_page_size = MEMFILE_PAGE_SIZE;

#ifdef USE_FSTATFS
    /*
     * Try to set the page size equal to the block size of the device.
     * Speeds up I/O a lot.
     * When recovering, the actual block size will be retrieved from block 0
     * in ml_recover().  The size used here may be wrong, therefore
     * mf_blocknr_max must be rounded up.
     */
    if (mfp->mf_fd >= 0
            && fstatfs(mfp->mf_fd, &stf, sizeof(struct statfs), 0) == 0
            && stf.F_BSIZE >= MIN_SWAP_PAGE_SIZE
            && stf.F_BSIZE <= MAX_SWAP_PAGE_SIZE)
        mfp->mf_page_size = stf.F_BSIZE;
#endif

    if (mfp->mf_fd < 0 || (flags & (O_TRUNC|O_EXCL))
                      || (size = lseek(mfp->mf_fd, (off_t)0L, SEEK_END)) <= 0)
        mfp->mf_blocknr_max = 0;        /* no file or empty file */
    else
        mfp->mf_blocknr_max = (blocknr_T)((size + mfp->mf_page_size - 1)
                                                         / mfp->mf_page_size);
    mfp->mf_blocknr_min = -1;
    mfp->mf_neg_count = 0;
    mfp->mf_infile_count = mfp->mf_blocknr_max;
    mfp->mf_used_count_max = p_mm * 1024 / mfp->mf_page_size;

    return mfp;
}

/*
 * Open a file for an existing memfile.  Used when updatecount set from 0 to
 * some value.
 * If the file already exists, this fails.
 * "fname" is the name of file to use (NULL means no file at all)
 * Note: "fname" must have been allocated, it is not copied!  If opening the
 * file fails, "fname" is freed.
 *
 * return value: FAIL if file could not be opened, OK otherwise
 */
    int
mf_open_file(mfp, fname)
    memfile_T   *mfp;
    char_u      *fname;
{
    mf_do_open(mfp, fname, O_RDWR|O_CREAT|O_EXCL); /* try to open the file */

    if (mfp->mf_fd < 0)
        return FAIL;

    mfp->mf_dirty = TRUE;
    return OK;
}

/*
 * close a memory file and delete the associated file if 'del_file' is TRUE
 */
    void
mf_close(mfp, del_file)
    memfile_T   *mfp;
    int         del_file;
{
    bhdr_T      *hp, *nextp;
    NR_TRANS    *tp, *tpnext;
    int         i;

    if (mfp == NULL)                /* safety check */
        return;
    if (mfp->mf_fd >= 0)
    {
        if (close(mfp->mf_fd) < 0)
            EMSG(_(e_swapclose));
    }
    if (del_file && mfp->mf_fname != NULL)
        mch_remove(mfp->mf_fname);
                                            /* free entries in used list */
    for (hp = mfp->mf_used_first; hp != NULL; hp = nextp)
    {
        total_mem_used -= hp->bh_page_count * mfp->mf_page_size;
        nextp = hp->bh_next;
        mf_free_bhdr(hp);
    }
    while (mfp->mf_free_first != NULL)      /* free entries in free list */
        vim_free(mf_rem_free(mfp));
    for (i = 0; i < MEMHASHSIZE; ++i)       /* free entries in trans lists */
        for (tp = mfp->mf_trans[i]; tp != NULL; tp = tpnext)
        {
            tpnext = tp->nt_next;
            vim_free(tp);
        }
    vim_free(mfp->mf_fname);
    vim_free(mfp->mf_ffname);
    vim_free(mfp);
}

/*
 * Close the swap file for a memfile.  Used when 'swapfile' is reset.
 */
    void
mf_close_file(buf, getlines)
    buf_T       *buf;
    int         getlines;       /* get all lines into memory? */
{
    memfile_T   *mfp;
    linenr_T    lnum;

    mfp = buf->b_ml.ml_mfp;
    if (mfp == NULL || mfp->mf_fd < 0)          /* nothing to close */
        return;

    if (getlines)
    {
        /* get all blocks in memory by accessing all lines (clumsy!) */
        dont_release = TRUE;
        for (lnum = 1; lnum <= buf->b_ml.ml_line_count; ++lnum)
            (void)ml_get_buf(buf, lnum, FALSE);
        dont_release = FALSE;
        /* TODO: should check if all blocks are really in core */
    }

    if (close(mfp->mf_fd) < 0)                  /* close the file */
        EMSG(_(e_swapclose));
    mfp->mf_fd = -1;

    if (mfp->mf_fname != NULL)
    {
        mch_remove(mfp->mf_fname);              /* delete the swap file */
        vim_free(mfp->mf_fname);
        vim_free(mfp->mf_ffname);
        mfp->mf_fname = NULL;
        mfp->mf_ffname = NULL;
    }
}

/*
 * Set new size for a memfile.  Used when block 0 of a swapfile has been read
 * and the size it indicates differs from what was guessed.
 */
    void
mf_new_page_size(mfp, new_size)
    memfile_T   *mfp;
    unsigned    new_size;
{
    /* Correct the memory used for block 0 to the new size, because it will be
     * freed with that size later on. */
    total_mem_used += new_size - mfp->mf_page_size;
    mfp->mf_page_size = new_size;
}

/*
 * get a new block
 *
 *   negative: TRUE if negative block number desired (data block)
 */
    bhdr_T *
mf_new(mfp, negative, page_count)
    memfile_T   *mfp;
    int         negative;
    int         page_count;
{
    bhdr_T    *hp;          /* new bhdr_T */
    bhdr_T    *freep;       /* first block in free list */
    char_u  *p;

    /*
     * If we reached the maximum size for the used memory blocks, release one
     * If a bhdr_T is returned, use it and adjust the page_count if necessary.
     */
    hp = mf_release(mfp, page_count);

/*
 * Decide on the number to use:
 * If there is a free block, use its number.
 * Otherwise use mf_block_min for a negative number, mf_block_max for
 * a positive number.
 */
    freep = mfp->mf_free_first;
    if (!negative && freep != NULL && freep->bh_page_count >= page_count)
    {
        /*
         * If the block in the free list has more pages, take only the number
         * of pages needed and allocate a new bhdr_T with data
         *
         * If the number of pages matches and mf_release did not return a bhdr_T,
         * use the bhdr_T from the free list and allocate the data
         *
         * If the number of pages matches and mf_release returned a bhdr_T,
         * just use the number and free the bhdr_T from the free list
         */
        if (freep->bh_page_count > page_count)
        {
            if (hp == NULL && (hp = mf_alloc_bhdr(mfp, page_count)) == NULL)
                return NULL;
            hp->bh_bnum = freep->bh_bnum;
            freep->bh_bnum += page_count;
            freep->bh_page_count -= page_count;
        }
        else if (hp == NULL)        /* need to allocate memory for this block */
        {
            if ((p = (char_u *)alloc(mfp->mf_page_size * page_count)) == NULL)
                return NULL;
            hp = mf_rem_free(mfp);
            hp->bh_data = p;
        }
        else                /* use the number, remove entry from free list */
        {
            freep = mf_rem_free(mfp);
            hp->bh_bnum = freep->bh_bnum;
            vim_free(freep);
        }
    }
    else        /* get a new number */
    {
        if (hp == NULL && (hp = mf_alloc_bhdr(mfp, page_count)) == NULL)
            return NULL;
        if (negative)
        {
            hp->bh_bnum = mfp->mf_blocknr_min--;
            mfp->mf_neg_count++;
        }
        else
        {
            hp->bh_bnum = mfp->mf_blocknr_max;
            mfp->mf_blocknr_max += page_count;
        }
    }
    hp->bh_flags = BH_LOCKED | BH_DIRTY;        /* new block is always dirty */
    mfp->mf_dirty = TRUE;
    hp->bh_page_count = page_count;
    mf_ins_used(mfp, hp);
    mf_ins_hash(mfp, hp);

    /*
     * Init the data to all zero, to avoid reading uninitialized data.
     * This also avoids that the passwd file ends up in the swap file!
     */
    (void)vim_memset((char *)(hp->bh_data), 0, (size_t)mfp->mf_page_size);

    return hp;
}

/*
 * get existing block 'nr' with 'page_count' pages
 *
 * Note: The caller should first check a negative nr with mf_trans_del()
 */
    bhdr_T *
mf_get(mfp, nr, page_count)
    memfile_T   *mfp;
    blocknr_T   nr;
    int         page_count;
{
    bhdr_T    *hp;
                                                /* doesn't exist */
    if (nr >= mfp->mf_blocknr_max || nr <= mfp->mf_blocknr_min)
        return NULL;

    /*
     * see if it is in the cache
     */
    hp = mf_find_hash(mfp, nr);
    if (hp == NULL)     /* not in the hash list */
    {
        if (nr < 0 || nr >= mfp->mf_infile_count)   /* can't be in the file */
            return NULL;

        /* could check here if the block is in the free list */

        /*
         * Check if we need to flush an existing block.
         * If so, use that block.
         * If not, allocate a new block.
         */
        hp = mf_release(mfp, page_count);
        if (hp == NULL && (hp = mf_alloc_bhdr(mfp, page_count)) == NULL)
            return NULL;

        hp->bh_bnum = nr;
        hp->bh_flags = 0;
        hp->bh_page_count = page_count;
        if (mf_read(mfp, hp) == FAIL)       /* cannot read the block! */
        {
            mf_free_bhdr(hp);
            return NULL;
        }
    }
    else
    {
        mf_rem_used(mfp, hp);   /* remove from list, insert in front below */
        mf_rem_hash(mfp, hp);
    }

    hp->bh_flags |= BH_LOCKED;
    mf_ins_used(mfp, hp);       /* put in front of used list */
    mf_ins_hash(mfp, hp);       /* put in front of hash list */

    return hp;
}

/*
 * release the block *hp
 *
 *   dirty: Block must be written to file later
 *   infile: Block should be in file (needed for recovery)
 *
 *  no return value, function cannot fail
 */
    void
mf_put(mfp, hp, dirty, infile)
    memfile_T   *mfp;
    bhdr_T      *hp;
    int         dirty;
    int         infile;
{
    int         flags;

    flags = hp->bh_flags;

    if ((flags & BH_LOCKED) == 0)
        EMSG(_("E293: block was not locked"));
    flags &= ~BH_LOCKED;
    if (dirty)
    {
        flags |= BH_DIRTY;
        mfp->mf_dirty = TRUE;
    }
    hp->bh_flags = flags;
    if (infile)
        mf_trans_add(mfp, hp);      /* may translate negative in positive nr */
}

/*
 * block *hp is no longer in used, may put it in the free list of memfile *mfp
 */
    void
mf_free(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    vim_free(hp->bh_data);      /* free the memory */
    mf_rem_hash(mfp, hp);       /* get *hp out of the hash list */
    mf_rem_used(mfp, hp);       /* get *hp out of the used list */
    if (hp->bh_bnum < 0)
    {
        vim_free(hp);           /* don't want negative numbers in free list */
        mfp->mf_neg_count--;
    }
    else
        mf_ins_free(mfp, hp);   /* put *hp in the free list */
}

#if defined(__MORPHOS__) && defined(__libnix__)
/* function is missing in MorphOS libnix version */
extern unsigned long *__stdfiledes;

    static unsigned long
fdtofh(int filedescriptor)
{
    return __stdfiledes[filedescriptor];
}
#endif

/*
 * Sync the memory file *mfp to disk.
 * Flags:
 *  MFS_ALL     If not given, blocks with negative numbers are not synced,
 *              even when they are dirty!
 *  MFS_STOP    Stop syncing when a character becomes available, but sync at
 *              least one block.
 *  MFS_FLUSH   Make sure buffers are flushed to disk, so they will survive a
 *              system crash.
 *  MFS_ZERO    Only write block 0.
 *
 * Return FAIL for failure, OK otherwise
 */
    int
mf_sync(mfp, flags)
    memfile_T   *mfp;
    int         flags;
{
    int         status;
    bhdr_T      *hp;
#if defined(SYNC_DUP_CLOSE) && !defined(MSDOS)
    int         fd;
#endif
    int         got_int_save = got_int;

    if (mfp->mf_fd < 0)     /* there is no file, nothing to do */
    {
        mfp->mf_dirty = FALSE;
        return FAIL;
    }

    /* Only a CTRL-C while writing will break us here, not one typed
     * previously. */
    got_int = FALSE;

    /*
     * sync from last to first (may reduce the probability of an inconsistent
     * file) If a write fails, it is very likely caused by a full filesystem.
     * Then we only try to write blocks within the existing file. If that also
     * fails then we give up.
     */
    status = OK;
    for (hp = mfp->mf_used_last; hp != NULL; hp = hp->bh_prev)
        if (((flags & MFS_ALL) || hp->bh_bnum >= 0)
                && (hp->bh_flags & BH_DIRTY)
                && (status == OK || (hp->bh_bnum >= 0
                    && hp->bh_bnum < mfp->mf_infile_count)))
        {
            if ((flags & MFS_ZERO) && hp->bh_bnum != 0)
                continue;
            if (mf_write(mfp, hp) == FAIL)
            {
                if (status == FAIL)     /* double error: quit syncing */
                    break;
                status = FAIL;
            }
            if (flags & MFS_STOP)
            {
                /* Stop when char available now. */
                if (ui_char_avail())
                    break;
            }
            else
                ui_breakcheck();
            if (got_int)
                break;
        }

    /*
     * If the whole list is flushed, the memfile is not dirty anymore.
     * In case of an error this flag is also set, to avoid trying all the time.
     */
    if (hp == NULL || status == FAIL)
        mfp->mf_dirty = FALSE;

    if ((flags & MFS_FLUSH) && *p_sws != NUL)
    {
#if defined(UNIX)
# ifdef HAVE_FSYNC
        /*
         * most Unixes have the very useful fsync() function, just what we need.
         * However, with OS/2 and EMX it is also available, but there are
         * reports of bad problems with it (a bug in HPFS.IFS).
         * So we disable use of it here in case someone tries to be smart
         * and changes os_os2_cfg.h... (even though there is no __EMX__ test
         * in the #if, as __EMX__ does not have sync(); we hope for a timely
         * sync from the system itself).
         */
#  if defined(__EMX__)
   error "Dont use fsync with EMX! Read emxdoc.doc or emxfix01.doc for info."
#  endif
        if (STRCMP(p_sws, "fsync") == 0)
        {
            if (fsync(mfp->mf_fd))
                status = FAIL;
        }
        else
# endif
            /* OpenNT is strictly POSIX (Benzinger) */
            /* Tandem/Himalaya NSK-OSS doesn't have sync() */
# if defined(__OPENNT) || defined(__TANDEM)
            fflush(NULL);
# else
            sync();
# endif
#endif
#ifdef VMS
        if (STRCMP(p_sws, "fsync") == 0)
        {
            if (fsync(mfp->mf_fd))
                status = FAIL;
        }
#endif
#ifdef MSDOS
        if (_dos_commit(mfp->mf_fd))
            status = FAIL;
#else
# ifdef SYNC_DUP_CLOSE
        /*
         * Win32 is a bit more work: Duplicate the file handle and close it.
         * This should flush the file to disk.
         */
        if ((fd = dup(mfp->mf_fd)) >= 0)
            close(fd);
# endif
#endif
#ifdef AMIGA
# if defined(__AROS__) || defined(__amigaos4__)
        if (fsync(mfp->mf_fd) != 0)
            status = FAIL;
# else
        /*
         * Flush() only exists for AmigaDos 2.0.
         * For 1.3 it should be done with close() + open(), but then the risk
         * is that the open() may fail and lose the file....
         */
#  ifdef FEAT_ARP
        if (dos2)
#  endif
#  ifdef SASC
        {
            struct UFB *fp = chkufb(mfp->mf_fd);

            if (fp != NULL)
                Flush(fp->ufbfh);
        }
#  else
#   if defined(_DCC) || defined(__GNUC__) || defined(__MORPHOS__)
        {
#    if defined(__GNUC__) && !defined(__MORPHOS__) && defined(__libnix__)
            /* Have function (in libnix at least),
             * but ain't got no prototype anywhere. */
            extern unsigned long fdtofh(int filedescriptor);
#    endif
#    if !defined(__libnix__)
            fflush(NULL);
#    else
            BPTR fh = (BPTR)fdtofh(mfp->mf_fd);

            if (fh != 0)
                Flush(fh);
#    endif
        }
#   else /* assume Manx */
            Flush(_devtab[mfp->mf_fd].fd);
#   endif
#  endif
# endif
#endif /* AMIGA */
    }

    got_int |= got_int_save;

    return status;
}

/*
 * For all blocks in memory file *mfp that have a positive block number set
 * the dirty flag.  These are blocks that need to be written to a newly
 * created swapfile.
 */
    void
mf_set_dirty(mfp)
    memfile_T   *mfp;
{
    bhdr_T      *hp;

    for (hp = mfp->mf_used_last; hp != NULL; hp = hp->bh_prev)
        if (hp->bh_bnum > 0)
            hp->bh_flags |= BH_DIRTY;
    mfp->mf_dirty = TRUE;
}

/*
 * insert block *hp in front of hashlist of memfile *mfp
 */
    static void
mf_ins_hash(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    bhdr_T      *hhp;
    int         hash;

    hash = MEMHASH(hp->bh_bnum);
    hhp = mfp->mf_hash[hash];
    hp->bh_hash_next = hhp;
    hp->bh_hash_prev = NULL;
    if (hhp != NULL)
        hhp->bh_hash_prev = hp;
    mfp->mf_hash[hash] = hp;
}

/*
 * remove block *hp from hashlist of memfile list *mfp
 */
    static void
mf_rem_hash(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    if (hp->bh_hash_prev == NULL)
        mfp->mf_hash[MEMHASH(hp->bh_bnum)] = hp->bh_hash_next;
    else
        hp->bh_hash_prev->bh_hash_next = hp->bh_hash_next;

    if (hp->bh_hash_next)
        hp->bh_hash_next->bh_hash_prev = hp->bh_hash_prev;
}

/*
 * look in hash lists of memfile *mfp for block header with number 'nr'
 */
    static bhdr_T *
mf_find_hash(mfp, nr)
    memfile_T   *mfp;
    blocknr_T   nr;
{
    bhdr_T      *hp;

    for (hp = mfp->mf_hash[MEMHASH(nr)]; hp != NULL; hp = hp->bh_hash_next)
        if (hp->bh_bnum == nr)
            break;
    return hp;
}

/*
 * insert block *hp in front of used list of memfile *mfp
 */
    static void
mf_ins_used(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    hp->bh_next = mfp->mf_used_first;
    mfp->mf_used_first = hp;
    hp->bh_prev = NULL;
    if (hp->bh_next == NULL)        /* list was empty, adjust last pointer */
        mfp->mf_used_last = hp;
    else
        hp->bh_next->bh_prev = hp;
    mfp->mf_used_count += hp->bh_page_count;
    total_mem_used += hp->bh_page_count * mfp->mf_page_size;
}

/*
 * remove block *hp from used list of memfile *mfp
 */
    static void
mf_rem_used(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    if (hp->bh_next == NULL)        /* last block in used list */
        mfp->mf_used_last = hp->bh_prev;
    else
        hp->bh_next->bh_prev = hp->bh_prev;
    if (hp->bh_prev == NULL)        /* first block in used list */
        mfp->mf_used_first = hp->bh_next;
    else
        hp->bh_prev->bh_next = hp->bh_next;
    mfp->mf_used_count -= hp->bh_page_count;
    total_mem_used -= hp->bh_page_count * mfp->mf_page_size;
}

/*
 * Release the least recently used block from the used list if the number
 * of used memory blocks gets to big.
 *
 * Return the block header to the caller, including the memory block, so
 * it can be re-used. Make sure the page_count is right.
 */
    static bhdr_T *
mf_release(mfp, page_count)
    memfile_T   *mfp;
    int         page_count;
{
    bhdr_T      *hp;
    int         need_release;
    buf_T       *buf;

    /* don't release while in mf_close_file() */
    if (dont_release)
        return NULL;

    /*
     * Need to release a block if the number of blocks for this memfile is
     * higher than the maximum or total memory used is over 'maxmemtot'
     */
    need_release = ((mfp->mf_used_count >= mfp->mf_used_count_max)
                                  || (total_mem_used >> 10) >= (long_u)p_mmt);

    /*
     * Try to create a swap file if the amount of memory used is getting too
     * high.
     */
    if (mfp->mf_fd < 0 && need_release && p_uc)
    {
        /* find for which buffer this memfile is */
        for (buf = firstbuf; buf != NULL; buf = buf->b_next)
            if (buf->b_ml.ml_mfp == mfp)
                break;
        if (buf != NULL && buf->b_may_swap)
            ml_open_file(buf);
    }

    /*
     * don't release a block if
     *  there is no file for this memfile
     * or
     *  the number of blocks for this memfile is lower than the maximum
     *    and
     *  total memory used is not up to 'maxmemtot'
     */
    if (mfp->mf_fd < 0 || !need_release)
        return NULL;

    for (hp = mfp->mf_used_last; hp != NULL; hp = hp->bh_prev)
        if (!(hp->bh_flags & BH_LOCKED))
            break;
    if (hp == NULL)     /* not a single one that can be released */
        return NULL;

    /*
     * If the block is dirty, write it.
     * If the write fails we don't free it.
     */
    if ((hp->bh_flags & BH_DIRTY) && mf_write(mfp, hp) == FAIL)
        return NULL;

    mf_rem_used(mfp, hp);
    mf_rem_hash(mfp, hp);

    /*
     * If a bhdr_T is returned, make sure that the page_count of bh_data is
     * right
     */
    if (hp->bh_page_count != page_count)
    {
        vim_free(hp->bh_data);
        if ((hp->bh_data = alloc(mfp->mf_page_size * page_count)) == NULL)
        {
            vim_free(hp);
            return NULL;
        }
        hp->bh_page_count = page_count;
    }
    return hp;
}

/*
 * release as many blocks as possible
 * Used in case of out of memory
 *
 * return TRUE if any memory was released
 */
    int
mf_release_all()
{
    buf_T       *buf;
    memfile_T   *mfp;
    bhdr_T      *hp;
    int         retval = FALSE;

    for (buf = firstbuf; buf != NULL; buf = buf->b_next)
    {
        mfp = buf->b_ml.ml_mfp;
        if (mfp != NULL)
        {
            /* If no swap file yet, may open one */
            if (mfp->mf_fd < 0 && buf->b_may_swap)
                ml_open_file(buf);

            /* only if there is a swapfile */
            if (mfp->mf_fd >= 0)
            {
                for (hp = mfp->mf_used_last; hp != NULL; )
                {
                    if (!(hp->bh_flags & BH_LOCKED)
                            && (!(hp->bh_flags & BH_DIRTY)
                                || mf_write(mfp, hp) != FAIL))
                    {
                        mf_rem_used(mfp, hp);
                        mf_rem_hash(mfp, hp);
                        mf_free_bhdr(hp);
                        hp = mfp->mf_used_last; /* re-start, list was changed */
                        retval = TRUE;
                    }
                    else
                        hp = hp->bh_prev;
                }
            }
        }
    }
    return retval;
}

/*
 * Allocate a block header and a block of memory for it
 */
    static bhdr_T *
mf_alloc_bhdr(mfp, page_count)
    memfile_T   *mfp;
    int         page_count;
{
    bhdr_T      *hp;

    if ((hp = (bhdr_T *)alloc((unsigned)sizeof(bhdr_T))) != NULL)
    {
        if ((hp->bh_data = (char_u *)alloc(mfp->mf_page_size * page_count))
                                                                      == NULL)
        {
            vim_free(hp);           /* not enough memory */
            return NULL;
        }
        hp->bh_page_count = page_count;
    }
    return hp;
}

/*
 * Free a block header and the block of memory for it
 */
    static void
mf_free_bhdr(hp)
    bhdr_T      *hp;
{
    vim_free(hp->bh_data);
    vim_free(hp);
}

/*
 * insert entry *hp in the free list
 */
    static void
mf_ins_free(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    hp->bh_next = mfp->mf_free_first;
    mfp->mf_free_first = hp;
}

/*
 * remove the first entry from the free list and return a pointer to it
 * Note: caller must check that mfp->mf_free_first is not NULL!
 */
    static bhdr_T *
mf_rem_free(mfp)
    memfile_T   *mfp;
{
    bhdr_T      *hp;

    hp = mfp->mf_free_first;
    mfp->mf_free_first = hp->bh_next;
    return hp;
}

/*
 * read a block from disk
 *
 * Return FAIL for failure, OK otherwise
 */
    static int
mf_read(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    off_t       offset;
    unsigned    page_size;
    unsigned    size;

    if (mfp->mf_fd < 0)     /* there is no file, can't read */
        return FAIL;

    page_size = mfp->mf_page_size;
    offset = (off_t)page_size * hp->bh_bnum;
    size = page_size * hp->bh_page_count;
    if (lseek(mfp->mf_fd, offset, SEEK_SET) != offset)
    {
        PERROR(_("E294: Seek error in swap file read"));
        return FAIL;
    }
    if ((unsigned)vim_read(mfp->mf_fd, hp->bh_data, size) != size)
    {
        PERROR(_("E295: Read error in swap file"));
        return FAIL;
    }
    return OK;
}

/*
 * write a block to disk
 *
 * Return FAIL for failure, OK otherwise
 */
    static int
mf_write(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    off_t       offset;     /* offset in the file */
    blocknr_T   nr;         /* block nr which is being written */
    bhdr_T      *hp2;
    unsigned    page_size;  /* number of bytes in a page */
    unsigned    page_count; /* number of pages written */
    unsigned    size;       /* number of bytes written */

    if (mfp->mf_fd < 0)     /* there is no file, can't write */
        return FAIL;

    if (hp->bh_bnum < 0)        /* must assign file block number */
        if (mf_trans_add(mfp, hp) == FAIL)
            return FAIL;

    page_size = mfp->mf_page_size;

    /*
     * We don't want gaps in the file. Write the blocks in front of *hp
     * to extend the file.
     * If block 'mf_infile_count' is not in the hash list, it has been
     * freed. Fill the space in the file with data from the current block.
     */
    for (;;)
    {
        nr = hp->bh_bnum;
        if (nr > mfp->mf_infile_count)          /* beyond end of file */
        {
            nr = mfp->mf_infile_count;
            hp2 = mf_find_hash(mfp, nr);        /* NULL catched below */
        }
        else
            hp2 = hp;

        offset = (off_t)page_size * nr;
        if (lseek(mfp->mf_fd, offset, SEEK_SET) != offset)
        {
            PERROR(_("E296: Seek error in swap file write"));
            return FAIL;
        }
        if (hp2 == NULL)            /* freed block, fill with dummy data */
            page_count = 1;
        else
            page_count = hp2->bh_page_count;
        size = page_size * page_count;
        if ((unsigned)vim_write(mfp->mf_fd,
             (hp2 == NULL ? hp : hp2)->bh_data, size) != size)
        {
            /*
             * Avoid repeating the error message, this mostly happens when the
             * disk is full. We give the message again only after a succesful
             * write or when hitting a key. We keep on trying, in case some
             * space becomes available.
             */
            if (!did_swapwrite_msg)
                EMSG(_("E297: Write error in swap file"));
            did_swapwrite_msg = TRUE;
            return FAIL;
        }
        did_swapwrite_msg = FALSE;
        if (hp2 != NULL)                    /* written a non-dummy block */
            hp2->bh_flags &= ~BH_DIRTY;
                                            /* appended to the file */
        if (nr + (blocknr_T)page_count > mfp->mf_infile_count)
            mfp->mf_infile_count = nr + page_count;
        if (nr == hp->bh_bnum)              /* written the desired block */
            break;
    }
    return OK;
}

/*
 * Make block number for *hp positive and add it to the translation list
 *
 * Return FAIL for failure, OK otherwise
 */
    static int
mf_trans_add(mfp, hp)
    memfile_T   *mfp;
    bhdr_T      *hp;
{
    bhdr_T      *freep;
    blocknr_T   new_bnum;
    int         hash;
    NR_TRANS    *np;
    int         page_count;

    if (hp->bh_bnum >= 0)                   /* it's already positive */
        return OK;

    if ((np = (NR_TRANS *)alloc((unsigned)sizeof(NR_TRANS))) == NULL)
        return FAIL;

/*
 * get a new number for the block.
 * If the first item in the free list has sufficient pages, use its number
 * Otherwise use mf_blocknr_max.
 */
    freep = mfp->mf_free_first;
    page_count = hp->bh_page_count;
    if (freep != NULL && freep->bh_page_count >= page_count)
    {
        new_bnum = freep->bh_bnum;
        /*
         * If the page count of the free block was larger, recude it.
         * If the page count matches, remove the block from the free list
         */
        if (freep->bh_page_count > page_count)
        {
            freep->bh_bnum += page_count;
            freep->bh_page_count -= page_count;
        }
        else
        {
            freep = mf_rem_free(mfp);
            vim_free(freep);
        }
    }
    else
    {
        new_bnum = mfp->mf_blocknr_max;
        mfp->mf_blocknr_max += page_count;
    }

    np->nt_old_bnum = hp->bh_bnum;          /* adjust number */
    np->nt_new_bnum = new_bnum;

    mf_rem_hash(mfp, hp);                   /* remove from old hash list */
    hp->bh_bnum = new_bnum;
    mf_ins_hash(mfp, hp);                   /* insert in new hash list */

    hash = MEMHASH(np->nt_old_bnum);        /* insert in trans list */
    np->nt_next = mfp->mf_trans[hash];
    mfp->mf_trans[hash] = np;
    if (np->nt_next != NULL)
        np->nt_next->nt_prev = np;
    np->nt_prev = NULL;

    return OK;
}

/*
 * Lookup a tranlation from the trans lists and delete the entry
 *
 * Return the positive new number when found, the old number when not found
 */
    blocknr_T
mf_trans_del(mfp, old_nr)
    memfile_T   *mfp;
    blocknr_T   old_nr;
{
    int         hash;
    NR_TRANS    *np;
    blocknr_T   new_bnum;

    hash = MEMHASH(old_nr);
    for (np = mfp->mf_trans[hash]; np != NULL; np = np->nt_next)
        if (np->nt_old_bnum == old_nr)
            break;
    if (np == NULL)             /* not found */
        return old_nr;

    mfp->mf_neg_count--;
    new_bnum = np->nt_new_bnum;
    if (np->nt_prev != NULL)            /* remove entry from the trans list */
        np->nt_prev->nt_next = np->nt_next;
    else
        mfp->mf_trans[hash] = np->nt_next;
    if (np->nt_next != NULL)
        np->nt_next->nt_prev = np->nt_prev;
    vim_free(np);

    return new_bnum;
}

/*
 * Set mfp->mf_ffname according to mfp->mf_fname and some other things.
 * Only called when creating or renaming the swapfile.  Either way it's a new
 * name so we must work out the full path name.
 */
    void
mf_set_ffname(mfp)
    memfile_T   *mfp;
{
    mfp->mf_ffname = FullName_save(mfp->mf_fname, FALSE);
}

/*
 * Make the name of the file used for the memfile a full path.
 * Used before doing a :cd
 */
    void
mf_fullname(mfp)
    memfile_T   *mfp;
{
    if (mfp != NULL && mfp->mf_fname != NULL && mfp->mf_ffname != NULL)
    {
        vim_free(mfp->mf_fname);
        mfp->mf_fname = mfp->mf_ffname;
        mfp->mf_ffname = NULL;
    }
}

/*
 * return TRUE if there are any translations pending for 'mfp'
 */
    int
mf_need_trans(mfp)
    memfile_T   *mfp;
{
    return (mfp->mf_fname != NULL && mfp->mf_neg_count > 0);
}

/*
 * Open a swap file for a memfile.
 * The "fname" must be in allocated memory, and is consumed (also when an
 * error occurs).
 */
    static void
mf_do_open(mfp, fname, flags)
    memfile_T   *mfp;
    char_u      *fname;
    int         flags;          /* flags for open() */
{
#ifdef HAVE_LSTAT
    struct stat sb;
#endif

    mfp->mf_fname = fname;

    /*
     * Get the full path name before the open, because this is
     * not possible after the open on the Amiga.
     * fname cannot be NameBuff, because it must have been allocated.
     */
    mf_set_ffname(mfp);
#if defined(MSDOS) || defined(MSWIN) || defined(RISCOS)
    /*
     * A ":!cd e:xxx" may change the directory without us knowning, use the
     * full pathname always.  Careful: This frees fname!
     */
    mf_fullname(mfp);
#endif

#ifdef HAVE_LSTAT
    /*
     * Extra security check: When creating a swap file it really shouldn't
     * exist yet.  If there is a symbolic link, this is most likely an attack.
     */
    if ((flags & O_CREAT) && mch_lstat((char *)mfp->mf_fname, &sb) >= 0)
    {
        mfp->mf_fd = -1;
        EMSG(_("E300: Swap file already exists (symlink attack?)"));
    }
    else
#endif
    {
        /*
         * try to open the file
         */
        flags |= O_EXTRA | O_NOFOLLOW;
#ifdef WIN32
        /* Prevent handle inheritance that cause problems with Cscope
         * (swap file may not be deleted if cscope connection was open after
         * the file) */
        flags |= O_NOINHERIT;
#endif
        mfp->mf_fd = mch_open_rw((char *)mfp->mf_fname, flags);
    }

    /*
     * If the file cannot be opened, use memory only
     */
    if (mfp->mf_fd < 0)
    {
        vim_free(mfp->mf_fname);
        vim_free(mfp->mf_ffname);
        mfp->mf_fname = NULL;
        mfp->mf_ffname = NULL;
    }
    else
        mch_hide(mfp->mf_fname);    /* try setting the 'hidden' flag */
}