tdb: Make robust against shrinking tdbs

[Samba.git] / lib / tdb / common / io.c

 /* 
   Unix SMB/CIFS implementation.

   trivial database library

   Copyright (C) Andrew Tridgell              1999-2005
   Copyright (C) Paul `Rusty' Russell              2000
   Copyright (C) Jeremy Allison                    2000-2003

     ** NOTE! The following LGPL license applies to the tdb
     ** library. This does NOT imply that all of Samba is released
     ** under the LGPL

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 3 of the License, or (at your option) any later version.

   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with this library; if not, see <http://www.gnu.org/licenses/>.
*/


#include "tdb_private.h"

/* check for an out of bounds access - if it is out of bounds then
   see if the database has been expanded by someone else and expand
   if necessary 
   note that "len" is the minimum length needed for the db
*/
static int tdb_oob(struct tdb_context *tdb, tdb_off_t len, int probe)
{
        struct stat st;
        if (len <= tdb->map_size)
                return 0;
        if (tdb->flags & TDB_INTERNAL) {
                if (!probe) {
                        /* Ensure ecode is set for log fn. */
                        tdb->ecode = TDB_ERR_IO;
                        TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_oob len %d beyond internal malloc size %d\n",
                                 (int)len, (int)tdb->map_size));
                }
                return -1;
        }

        if (fstat(tdb->fd, &st) == -1) {
                tdb->ecode = TDB_ERR_IO;
                return -1;
        }

        /* Unmap, update size, remap */
        if (tdb_munmap(tdb) == -1) {
                tdb->ecode = TDB_ERR_IO;
                return -1;
        }
        tdb->map_size = st.st_size;
        tdb_mmap(tdb);

        if (st.st_size < (size_t)len) {
                if (!probe) {
                        /* Ensure ecode is set for log fn. */
                        tdb->ecode = TDB_ERR_IO;
                        TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_oob len %d beyond eof at %d\n",
                                 (int)len, (int)st.st_size));
                }
                return -1;
        }

        return 0;
}

/* write a lump of data at a specified offset */
static int tdb_write(struct tdb_context *tdb, tdb_off_t off, 
                     const void *buf, tdb_len_t len)
{
        if (len == 0) {
                return 0;
        }

        if (tdb->read_only || tdb->traverse_read) {
                tdb->ecode = TDB_ERR_RDONLY;
                return -1;
        }

        if (tdb->methods->tdb_oob(tdb, off + len, 0) != 0)
                return -1;

        if (tdb->map_ptr) {
                memcpy(off + (char *)tdb->map_ptr, buf, len);
        } else {
                ssize_t written = pwrite(tdb->fd, buf, len, off);
                if ((written != (ssize_t)len) && (written != -1)) {
                        /* try once more */
                        tdb->ecode = TDB_ERR_IO;
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_write: wrote only "
                                 "%d of %d bytes at %d, trying once more\n",
                                 (int)written, len, off));
                        written = pwrite(tdb->fd, (const char *)buf+written,
                                         len-written,
                                         off+written);
                }
                if (written == -1) {
                        /* Ensure ecode is set for log fn. */
                        tdb->ecode = TDB_ERR_IO;
                        TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_write failed at %d "
                                 "len=%d (%s)\n", off, len, strerror(errno)));
                        return -1;
                } else if (written != (ssize_t)len) {
                        tdb->ecode = TDB_ERR_IO;
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "tdb_write: failed to "
                                 "write %d bytes at %d in two attempts\n",
                                 len, off));
                        return -1;
                }
        }
        return 0;
}

/* Endian conversion: we only ever deal with 4 byte quantities */
void *tdb_convert(void *buf, uint32_t size)
{
        uint32_t i, *p = (uint32_t *)buf;
        for (i = 0; i < size / 4; i++)
                p[i] = TDB_BYTEREV(p[i]);
        return buf;
}


/* read a lump of data at a specified offset, maybe convert */
static int tdb_read(struct tdb_context *tdb, tdb_off_t off, void *buf, 
                    tdb_len_t len, int cv)
{
        if (tdb->methods->tdb_oob(tdb, off + len, 0) != 0) {
                return -1;
        }

        if (tdb->map_ptr) {
                memcpy(buf, off + (char *)tdb->map_ptr, len);
        } else {
                ssize_t ret = pread(tdb->fd, buf, len, off);
                if (ret != (ssize_t)len) {
                        /* Ensure ecode is set for log fn. */
                        tdb->ecode = TDB_ERR_IO;
                        TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_read failed at %d "
                                 "len=%d ret=%d (%s) map_size=%d\n",
                                 (int)off, (int)len, (int)ret, strerror(errno),
                                 (int)tdb->map_size));
                        return -1;
                }
        }
        if (cv) {
                tdb_convert(buf, len);
        }
        return 0;
}



/*
  do an unlocked scan of the hash table heads to find the next non-zero head. The value
  will then be confirmed with the lock held
*/              
static void tdb_next_hash_chain(struct tdb_context *tdb, uint32_t *chain)
{
        uint32_t h = *chain;
        if (tdb->map_ptr) {
                for (;h < tdb->header.hash_size;h++) {
                        if (0 != *(uint32_t *)(TDB_HASH_TOP(h) + (unsigned char *)tdb->map_ptr)) {
                                break;
                        }
                }
        } else {
                uint32_t off=0;
                for (;h < tdb->header.hash_size;h++) {
                        if (tdb_ofs_read(tdb, TDB_HASH_TOP(h), &off) != 0 || off != 0) {
                                break;
                        }
                }
        }
        (*chain) = h;
}


int tdb_munmap(struct tdb_context *tdb)
{
        if (tdb->flags & TDB_INTERNAL)
                return 0;

#ifdef HAVE_MMAP
        if (tdb->map_ptr) {
                int ret;

                ret = munmap(tdb->map_ptr, tdb->map_size);
                if (ret != 0)
                        return ret;
        }
#endif
        tdb->map_ptr = NULL;
        return 0;
}

void tdb_mmap(struct tdb_context *tdb)
{
        if (tdb->flags & TDB_INTERNAL)
                return;

#ifdef HAVE_MMAP
        if (!(tdb->flags & TDB_NOMMAP)) {
                tdb->map_ptr = mmap(NULL, tdb->map_size, 
                                    PROT_READ|(tdb->read_only? 0:PROT_WRITE), 
                                    MAP_SHARED|MAP_FILE, tdb->fd, 0);

                /*
                 * NB. When mmap fails it returns MAP_FAILED *NOT* NULL !!!!
                 */

                if (tdb->map_ptr == MAP_FAILED) {
                        tdb->map_ptr = NULL;
                        TDB_LOG((tdb, TDB_DEBUG_WARNING, "tdb_mmap failed for size %d (%s)\n", 
                                 tdb->map_size, strerror(errno)));
                }
        } else {
                tdb->map_ptr = NULL;
        }
#else
        tdb->map_ptr = NULL;
#endif
}

/* expand a file.  we prefer to use ftruncate, as that is what posix
  says to use for mmap expansion */
static int tdb_expand_file(struct tdb_context *tdb, tdb_off_t size, tdb_off_t addition)
{
        char buf[8192];

        if (tdb->read_only || tdb->traverse_read) {
                tdb->ecode = TDB_ERR_RDONLY;
                return -1;
        }

        if (ftruncate(tdb->fd, size+addition) == -1) {
                char b = 0;
                ssize_t written = pwrite(tdb->fd,  &b, 1, (size+addition) - 1);
                if (written == 0) {
                        /* try once more, potentially revealing errno */
                        written = pwrite(tdb->fd,  &b, 1, (size+addition) - 1);
                }
                if (written == 0) {
                        /* again - give up, guessing errno */
                        errno = ENOSPC;
                }
                if (written != 1) {
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "expand_file to %d failed (%s)\n", 
                                 size+addition, strerror(errno)));
                        return -1;
                }
        }

        /* now fill the file with something. This ensures that the
           file isn't sparse, which would be very bad if we ran out of
           disk. This must be done with write, not via mmap */
        memset(buf, TDB_PAD_BYTE, sizeof(buf));
        while (addition) {
                size_t n = addition>sizeof(buf)?sizeof(buf):addition;
                ssize_t written = pwrite(tdb->fd, buf, n, size);
                if (written == 0) {
                        /* prevent infinite loops: try _once_ more */
                        written = pwrite(tdb->fd, buf, n, size);
                }
                if (written == 0) {
                        /* give up, trying to provide a useful errno */
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "expand_file write "
                                "returned 0 twice: giving up!\n"));
                        errno = ENOSPC;
                        return -1;
                } else if (written == -1) {
                        TDB_LOG((tdb, TDB_DEBUG_FATAL, "expand_file write of "
                                 "%d bytes failed (%s)\n", (int)n,
                                 strerror(errno)));
                        return -1;
                } else if (written != n) {
                        TDB_LOG((tdb, TDB_DEBUG_WARNING, "expand_file: wrote "
                                 "only %d of %d bytes - retrying\n", (int)written,
                                 (int)n));
                }
                addition -= written;
                size += written;
        }
        return 0;
}


/* expand the database at least size bytes by expanding the underlying
   file and doing the mmap again if necessary */
int tdb_expand(struct tdb_context *tdb, tdb_off_t size)
{
        struct tdb_record rec;
        tdb_off_t offset, new_size, top_size, map_size;

        if (tdb_lock(tdb, -1, F_WRLCK) == -1) {
                TDB_LOG((tdb, TDB_DEBUG_ERROR, "lock failed in tdb_expand\n"));
                return -1;
        }

        /* must know about any previous expansions by another process */
        tdb->methods->tdb_oob(tdb, tdb->map_size + 1, 1);

        /* limit size in order to avoid using up huge amounts of memory for
         * in memory tdbs if an oddball huge record creeps in */
        if (size > 100 * 1024) {
                top_size = tdb->map_size + size * 2;
        } else {
                top_size = tdb->map_size + size * 100;
        }

        /* always make room for at least top_size more records, and at
           least 25% more space. if the DB is smaller than 100MiB,
           otherwise grow it by 10% only. */
        if (tdb->map_size > 100 * 1024 * 1024) {
                map_size = tdb->map_size * 1.10;
        } else {
                map_size = tdb->map_size * 1.25;
        }

        /* Round the database up to a multiple of the page size */
        new_size = MAX(top_size, map_size);
        size = TDB_ALIGN(new_size, tdb->page_size) - tdb->map_size;

        if (!(tdb->flags & TDB_INTERNAL))
                tdb_munmap(tdb);

        /*
         * We must ensure the file is unmapped before doing this
         * to ensure consistency with systems like OpenBSD where
         * writes and mmaps are not consistent.
         */

        /* expand the file itself */
        if (!(tdb->flags & TDB_INTERNAL)) {
                if (tdb->methods->tdb_expand_file(tdb, tdb->map_size, size) != 0)
                        goto fail;
        }

        tdb->map_size += size;

        if (tdb->flags & TDB_INTERNAL) {
                char *new_map_ptr = (char *)realloc(tdb->map_ptr,
                                                    tdb->map_size);
                if (!new_map_ptr) {
                        tdb->map_size -= size;
                        goto fail;
                }
                tdb->map_ptr = new_map_ptr;
        } else {
                /*
                 * We must ensure the file is remapped before adding the space
                 * to ensure consistency with systems like OpenBSD where
                 * writes and mmaps are not consistent.
                 */

                /* We're ok if the mmap fails as we'll fallback to read/write */
                tdb_mmap(tdb);
        }

        /* form a new freelist record */
        memset(&rec,'\0',sizeof(rec));
        rec.rec_len = size - sizeof(rec);

        /* link it into the free list */
        offset = tdb->map_size - size;
        if (tdb_free(tdb, offset, &rec) == -1)
                goto fail;

        tdb_unlock(tdb, -1, F_WRLCK);
        return 0;
 fail:
        tdb_unlock(tdb, -1, F_WRLCK);
        return -1;
}

/* read/write a tdb_off_t */
int tdb_ofs_read(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d)
{
        return tdb->methods->tdb_read(tdb, offset, (char*)d, sizeof(*d), DOCONV());
}

int tdb_ofs_write(struct tdb_context *tdb, tdb_off_t offset, tdb_off_t *d)
{
        tdb_off_t off = *d;
        return tdb->methods->tdb_write(tdb, offset, CONVERT(off), sizeof(*d));
}


/* read a lump of data, allocating the space for it */
unsigned char *tdb_alloc_read(struct tdb_context *tdb, tdb_off_t offset, tdb_len_t len)
{
        unsigned char *buf;

        /* some systems don't like zero length malloc */

        if (!(buf = (unsigned char *)malloc(len ? len : 1))) {
                /* Ensure ecode is set for log fn. */
                tdb->ecode = TDB_ERR_OOM;
                TDB_LOG((tdb, TDB_DEBUG_ERROR,"tdb_alloc_read malloc failed len=%d (%s)\n",
                           len, strerror(errno)));
                return NULL;
        }
        if (tdb->methods->tdb_read(tdb, offset, buf, len, 0) == -1) {
                SAFE_FREE(buf);
                return NULL;
        }
        return buf;
}

/* Give a piece of tdb data to a parser */

int tdb_parse_data(struct tdb_context *tdb, TDB_DATA key,
                   tdb_off_t offset, tdb_len_t len,
                   int (*parser)(TDB_DATA key, TDB_DATA data,
                                 void *private_data),
                   void *private_data)
{
        TDB_DATA data;
        int result;

        data.dsize = len;

        if ((tdb->transaction == NULL) && (tdb->map_ptr != NULL)) {
                /*
                 * Optimize by avoiding the malloc/memcpy/free, point the
                 * parser directly at the mmap area.
                 */
                if (tdb->methods->tdb_oob(tdb, offset+len, 0) != 0) {
                        return -1;
                }
                data.dptr = offset + (unsigned char *)tdb->map_ptr;
                return parser(key, data, private_data);
        }

        if (!(data.dptr = tdb_alloc_read(tdb, offset, len))) {
                return -1;
        }

        result = parser(key, data, private_data);
        free(data.dptr);
        return result;
}

/* read/write a record */
int tdb_rec_read(struct tdb_context *tdb, tdb_off_t offset, struct tdb_record *rec)
{
        if (tdb->methods->tdb_read(tdb, offset, rec, sizeof(*rec),DOCONV()) == -1)
                return -1;
        if (TDB_BAD_MAGIC(rec)) {
                /* Ensure ecode is set for log fn. */
                tdb->ecode = TDB_ERR_CORRUPT;
                TDB_LOG((tdb, TDB_DEBUG_FATAL,"tdb_rec_read bad magic 0x%x at offset=%d\n", rec->magic, offset));
                return -1;
        }
        return tdb->methods->tdb_oob(tdb, rec->next+sizeof(*rec), 0);
}

int tdb_rec_write(struct tdb_context *tdb, tdb_off_t offset, struct tdb_record *rec)
{
        struct tdb_record r = *rec;
        return tdb->methods->tdb_write(tdb, offset, CONVERT(r), sizeof(r));
}

static const struct tdb_methods io_methods = {
        tdb_read,
        tdb_write,
        tdb_next_hash_chain,
        tdb_oob,
        tdb_expand_file,
};

/*
  initialise the default methods table
*/
void tdb_io_init(struct tdb_context *tdb)
{
        tdb->methods = &io_methods;
}