block.c - qemu - Git at Google

 /*
  * QEMU System Emulator block driver
  *
  * Copyright (c) 2003 Fabrice Bellard
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
  * in the Software without restriction, including without limitation the rights
  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  * copies of the Software, and to permit persons to whom the Software is
  * furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice shall be included in
  * all copies or substantial portions of the Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 #include "vl.h"

 #ifndef _WIN32
 #include <sys/mman.h>
 #endif

 #include "cow.h"

 struct BlockDriverState {
     int fd; /* if -1, only COW mappings */
     int64_t total_sectors;
     int read_only; /* if true, the media is read only */
     int inserted; /* if true, the media is present */
     int removable; /* if true, the media can be removed */
     int locked;    /* if true, the media cannot temporarily be ejected */
     /* event callback when inserting/removing */
     void (*change_cb)(void *opaque);
     void *change_opaque;

     uint8_t *cow_bitmap; /* if non NULL, COW mappings are used first */
     uint8_t *cow_bitmap_addr; /* mmap address of cow_bitmap */
     int cow_bitmap_size;
     int cow_fd;
     int64_t cow_sectors_offset;
     int boot_sector_enabled;
     uint8_t boot_sector_data[512];

     char filename[1024];

     /* NOTE: the following infos are only hints for real hardware
        drivers. They are not used by the block driver */
     int cyls, heads, secs;
     int type;
     char device_name[32];
     BlockDriverState *next;
 };

 static BlockDriverState *bdrv_first;

 /* create a new block device (by default it is empty) */
 BlockDriverState *bdrv_new(const char *device_name)
 {
     BlockDriverState **pbs, *bs;

     bs = qemu_mallocz(sizeof(BlockDriverState));
     if(!bs)
         return NULL;
     pstrcpy(bs->device_name, sizeof(bs->device_name), device_name);
     /* insert at the end */
     pbs = &bdrv_first;
     while (*pbs != NULL)
         pbs = &(*pbs)->next;
     *pbs = bs;
     return bs;
 }

 int bdrv_open(BlockDriverState *bs, const char *filename, int snapshot)
 {
     int fd;
     int64_t size;
     struct cow_header_v2 cow_header;
 #ifndef _WIN32
     char template[] = "/tmp/vl.XXXXXX";
     int cow_fd;
     struct stat st;
 #endif

     bs->read_only = 0;
     bs->fd = -1;
     bs->cow_fd = -1;
     bs->cow_bitmap = NULL;
     strcpy(bs->filename, filename);

     /* open standard HD image */
 #ifdef _WIN32
     fd = open(filename, O_RDWR | O_BINARY);
 #else
     fd = open(filename, O_RDWR | O_LARGEFILE);
 #endif
     if (fd < 0) {
         /* read only image on disk */
 #ifdef _WIN32
         fd = open(filename, O_RDONLY | O_BINARY);
 #else
         fd = open(filename, O_RDONLY | O_LARGEFILE);
 #endif
         if (fd < 0) {
             perror(filename);
             goto fail;
         }
         if (!snapshot)
             bs->read_only = 1;
     }
     bs->fd = fd;

     /* see if it is a cow image */
     if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) {
         fprintf(stderr, "%s: could not read header\n", filename);
         goto fail;
     }
 #ifndef _WIN32
     if (be32_to_cpu(cow_header.magic) == COW_MAGIC &&
         be32_to_cpu(cow_header.version) == COW_VERSION) {
         /* cow image found */
         size = cow_header.size;
 #ifndef WORDS_BIGENDIAN
         size = bswap64(size);
 #endif
         bs->total_sectors = size / 512;

         bs->cow_fd = fd;
         bs->fd = -1;
         if (cow_header.backing_file[0] != '\0') {
             if (stat(cow_header.backing_file, &st) != 0) {
                 fprintf(stderr, "%s: could not find original disk image '%s'\n", filename, cow_header.backing_file);
                 goto fail;
             }
             if (st.st_mtime != be32_to_cpu(cow_header.mtime)) {
                 fprintf(stderr, "%s: original raw disk image '%s' does not match saved timestamp\n", filename, cow_header.backing_file);
                 goto fail;
             }
             fd = open(cow_header.backing_file, O_RDONLY | O_LARGEFILE);
             if (fd < 0)
                 goto fail;
             bs->fd = fd;
         }
         /* mmap the bitmap */
         bs->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
         bs->cow_bitmap_addr = mmap(get_mmap_addr(bs->cow_bitmap_size),
                                    bs->cow_bitmap_size,
                                    PROT_READ | PROT_WRITE,
                                    MAP_SHARED, bs->cow_fd, 0);
         if (bs->cow_bitmap_addr == MAP_FAILED)
             goto fail;
         bs->cow_bitmap = bs->cow_bitmap_addr + sizeof(cow_header);
         bs->cow_sectors_offset = (bs->cow_bitmap_size + 511) & ~511;
         snapshot = 0;
     } else
 #endif
     {
         /* standard raw image */
         size = lseek64(fd, 0, SEEK_END);
         bs->total_sectors = size / 512;
         bs->fd = fd;
     }

 #ifndef _WIN32
     if (snapshot) {
         /* create a temporary COW file */
         cow_fd = mkstemp64(template);
         if (cow_fd < 0)
             goto fail;
         bs->cow_fd = cow_fd;
 	unlink(template);

         /* just need to allocate bitmap */
         bs->cow_bitmap_size = (bs->total_sectors + 7) >> 3;
         bs->cow_bitmap_addr = mmap(get_mmap_addr(bs->cow_bitmap_size),
                                    bs->cow_bitmap_size,
                                    PROT_READ | PROT_WRITE,
                                    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
         if (bs->cow_bitmap_addr == MAP_FAILED)
             goto fail;
         bs->cow_bitmap = bs->cow_bitmap_addr;
         bs->cow_sectors_offset = 0;
     }
 #endif

     bs->inserted = 1;

     /* call the change callback */
     if (bs->change_cb)
         bs->change_cb(bs->change_opaque);

     return 0;
  fail:
     bdrv_close(bs);
     return -1;
 }

 void bdrv_close(BlockDriverState *bs)
 {
     if (bs->inserted) {
 #ifndef _WIN32
         /* we unmap the mapping so that it is written to the COW file */
         if (bs->cow_bitmap_addr)
             munmap(bs->cow_bitmap_addr, bs->cow_bitmap_size);
 #endif
         if (bs->cow_fd >= 0)
             close(bs->cow_fd);
         if (bs->fd >= 0)
             close(bs->fd);
         bs->inserted = 0;

         /* call the change callback */
         if (bs->change_cb)
             bs->change_cb(bs->change_opaque);
     }
 }

 void bdrv_delete(BlockDriverState *bs)
 {
     bdrv_close(bs);
     qemu_free(bs);
 }

 static inline void set_bit(uint8_t *bitmap, int64_t bitnum)
 {
     bitmap[bitnum / 8] |= (1 << (bitnum%8));
 }

 static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum)
 {
     return !!(bitmap[bitnum / 8] & (1 << (bitnum%8)));
 }


 /* Return true if first block has been changed (ie. current version is
  * in COW file).  Set the number of continuous blocks for which that
  * is true. */
 static int is_changed(uint8_t *bitmap,
                       int64_t sector_num, int nb_sectors,
                       int *num_same)
 {
     int changed;

     if (!bitmap || nb_sectors == 0) {
 	*num_same = nb_sectors;
 	return 0;
     }

     changed = is_bit_set(bitmap, sector_num);
     for (*num_same = 1; *num_same < nb_sectors; (*num_same)++) {
 	if (is_bit_set(bitmap, sector_num + *num_same) != changed)
 	    break;
     }

     return changed;
 }

 /* commit COW file into the raw image */
 int bdrv_commit(BlockDriverState *bs)
 {
     int64_t i;
     uint8_t *cow_bitmap;

     if (!bs->inserted)
         return -1;

     if (!bs->cow_bitmap) {
 	fprintf(stderr, "Already committed to %s\n", bs->filename);
 	return 0;
     }

     if (bs->read_only) {
 	fprintf(stderr, "Can't commit to %s: read-only\n", bs->filename);
 	return -1;
     }

     cow_bitmap = bs->cow_bitmap;
     for (i = 0; i < bs->total_sectors; i++) {
 	if (is_bit_set(cow_bitmap, i)) {
 	    unsigned char sector[512];
 	    if (bdrv_read(bs, i, sector, 1) != 0) {
 		fprintf(stderr, "Error reading sector %lli: aborting commit\n",
 			(long long)i);
 		return -1;
 	    }

 	    /* Make bdrv_write write to real file for a moment. */
 	    bs->cow_bitmap = NULL;
 	    if (bdrv_write(bs, i, sector, 1) != 0) {
 		fprintf(stderr, "Error writing sector %lli: aborting commit\n",
 			(long long)i);
 		bs->cow_bitmap = cow_bitmap;
 		return -1;
 	    }
 	    bs->cow_bitmap = cow_bitmap;
 	}
     }
     fprintf(stderr, "Committed snapshot to %s\n", bs->filename);
     return 0;
 }

 /* return -1 if error */
 int bdrv_read(BlockDriverState *bs, int64_t sector_num,
               uint8_t *buf, int nb_sectors)
 {
     int ret, n, fd;
     int64_t offset;

     if (!bs->inserted)
         return -1;

     while (nb_sectors > 0) {
         if (is_changed(bs->cow_bitmap, sector_num, nb_sectors, &n)) {
             fd = bs->cow_fd;
             offset = bs->cow_sectors_offset;
         } else if (sector_num == 0 && bs->boot_sector_enabled) {
             memcpy(buf, bs->boot_sector_data, 512);
             n = 1;
             goto next;
         } else {
             fd = bs->fd;
             offset = 0;
         }

         if (fd < 0) {
             /* no file, just return empty sectors */
             memset(buf, 0, n * 512);
         } else {
             offset += sector_num * 512;
             lseek64(fd, offset, SEEK_SET);
             ret = read(fd, buf, n * 512);
             if (ret != n * 512) {
                 return -1;
             }
         }
     next:
         nb_sectors -= n;
         sector_num += n;
         buf += n * 512;
     }
     return 0;
 }

 /* return -1 if error */
 int bdrv_write(BlockDriverState *bs, int64_t sector_num,
                const uint8_t *buf, int nb_sectors)
 {
     int ret, fd, i;
     int64_t offset, retl;

     if (!bs->inserted)
         return -1;
     if (bs->read_only)
         return -1;

     if (bs->cow_bitmap) {
         fd = bs->cow_fd;
         offset = bs->cow_sectors_offset;
     } else {
         fd = bs->fd;
         offset = 0;
     }

     offset += sector_num * 512;
     retl = lseek64(fd, offset, SEEK_SET);
     if (retl == -1) {
         return -1;
     }
     ret = write(fd, buf, nb_sectors * 512);
     if (ret != nb_sectors * 512) {
         return -1;
     }

     if (bs->cow_bitmap) {
 	for (i = 0; i < nb_sectors; i++)
 	    set_bit(bs->cow_bitmap, sector_num + i);
     }
     return 0;
 }

 void bdrv_get_geometry(BlockDriverState *bs, int64_t *nb_sectors_ptr)
 {
     *nb_sectors_ptr = bs->total_sectors;
 }

 /* force a given boot sector. */
 void bdrv_set_boot_sector(BlockDriverState *bs, const uint8_t *data, int size)
 {
     bs->boot_sector_enabled = 1;
     if (size > 512)
         size = 512;
     memcpy(bs->boot_sector_data, data, size);
     memset(bs->boot_sector_data + size, 0, 512 - size);
 }

 void bdrv_set_geometry_hint(BlockDriverState *bs,
                             int cyls, int heads, int secs)
 {
     bs->cyls = cyls;
     bs->heads = heads;
     bs->secs = secs;
 }

 void bdrv_set_type_hint(BlockDriverState *bs, int type)
 {
     bs->type = type;
     bs->removable = ((type == BDRV_TYPE_CDROM ||
                       type == BDRV_TYPE_FLOPPY));
 }

 void bdrv_get_geometry_hint(BlockDriverState *bs,
                             int *pcyls, int *pheads, int *psecs)
 {
     *pcyls = bs->cyls;
     *pheads = bs->heads;
     *psecs = bs->secs;
 }

 int bdrv_get_type_hint(BlockDriverState *bs)
 {
     return bs->type;
 }

 int bdrv_is_removable(BlockDriverState *bs)
 {
     return bs->removable;
 }

 int bdrv_is_read_only(BlockDriverState *bs)
 {
     return bs->read_only;
 }

 int bdrv_is_inserted(BlockDriverState *bs)
 {
     return bs->inserted;
 }

 int bdrv_is_locked(BlockDriverState *bs)
 {
     return bs->locked;
 }

 void bdrv_set_locked(BlockDriverState *bs, int locked)
 {
     bs->locked = locked;
 }

 void bdrv_set_change_cb(BlockDriverState *bs,
                         void (*change_cb)(void *opaque), void *opaque)
 {
     bs->change_cb = change_cb;
     bs->change_opaque = opaque;
 }

 BlockDriverState *bdrv_find(const char *name)
 {
     BlockDriverState *bs;

     for (bs = bdrv_first; bs != NULL; bs = bs->next) {
         if (!strcmp(name, bs->device_name))
             return bs;
     }
     return NULL;
 }

 void bdrv_info(void)
 {
     BlockDriverState *bs;

     for (bs = bdrv_first; bs != NULL; bs = bs->next) {
         term_printf("%s:", bs->device_name);
         term_printf(" type=");
         switch(bs->type) {
         case BDRV_TYPE_HD:
             term_printf("hd");
             break;
         case BDRV_TYPE_CDROM:
             term_printf("cdrom");
             break;
         case BDRV_TYPE_FLOPPY:
             term_printf("floppy");
             break;
         }
         term_printf(" removable=%d", bs->removable);
         if (bs->removable) {
             term_printf(" locked=%d", bs->locked);
         }
         if (bs->inserted) {
             term_printf(" file=%s", bs->filename);
             term_printf(" ro=%d", bs->read_only);
         } else {
             term_printf(" [not inserted]");
         }
         term_printf("\n");
     }
 }
	/*
	* QEMU System Emulator block driver
	*
	* Copyright (c) 2003 Fabrice Bellard
	*
	* Permission is hereby granted, free of charge, to any person obtaining a copy
	* of this software and associated documentation files (the "Software"), to deal
	* in the Software without restriction, including without limitation the rights
	* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	* copies of the Software, and to permit persons to whom the Software is
	* furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice shall be included in
	* all copies or substantial portions of the Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	* THE SOFTWARE.
	*/
	#include "vl.h"

	#ifndef _WIN32
	#include <sys/mman.h>
	#endif

	#include "cow.h"

	struct BlockDriverState {
	int fd; /* if -1, only COW mappings */
	int64_t total_sectors;
	int read_only; /* if true, the media is read only */
	int inserted; /* if true, the media is present */
	int removable; /* if true, the media can be removed */
	int locked; /* if true, the media cannot temporarily be ejected */
	/* event callback when inserting/removing */
	void (change_cb)(void opaque);
	void *change_opaque;

	uint8_t cow_bitmap; / if non NULL, COW mappings are used first */
	uint8_t cow_bitmap_addr; / mmap address of cow_bitmap */
	int cow_bitmap_size;
	int cow_fd;
	int64_t cow_sectors_offset;
	int boot_sector_enabled;
	uint8_t boot_sector_data[512];

	char filename[1024];

	/* NOTE: the following infos are only hints for real hardware
	drivers. They are not used by the block driver */
	int cyls, heads, secs;
	int type;
	char device_name[32];
	BlockDriverState *next;
	};

	static BlockDriverState *bdrv_first;

	/* create a new block device (by default it is empty) */
	BlockDriverState bdrv_new(const char device_name)
	{
	BlockDriverState *pbs, bs;

	bs = qemu_mallocz(sizeof(BlockDriverState));
	if(!bs)
	return NULL;
	pstrcpy(bs->device_name, sizeof(bs->device_name), device_name);
	/* insert at the end */
	pbs = &bdrv_first;
	while (*pbs != NULL)
	pbs = &(*pbs)->next;
	*pbs = bs;
	return bs;
	}

	int bdrv_open(BlockDriverState bs, const char filename, int snapshot)
	{
	int fd;
	int64_t size;
	struct cow_header_v2 cow_header;
	#ifndef _WIN32
	char template[] = "/tmp/vl.XXXXXX";
	int cow_fd;
	struct stat st;
	#endif

	bs->read_only = 0;
	bs->fd = -1;
	bs->cow_fd = -1;
	bs->cow_bitmap = NULL;
	strcpy(bs->filename, filename);

	/* open standard HD image */
	#ifdef _WIN32
	fd = open(filename, O_RDWR \| O_BINARY);
	#else
	fd = open(filename, O_RDWR \| O_LARGEFILE);
	#endif
	if (fd < 0) {
	/* read only image on disk */
	#ifdef _WIN32
	fd = open(filename, O_RDONLY \| O_BINARY);
	#else
	fd = open(filename, O_RDONLY \| O_LARGEFILE);
	#endif
	if (fd < 0) {
	perror(filename);
	goto fail;
	}
	if (!snapshot)
	bs->read_only = 1;
	}
	bs->fd = fd;

	/* see if it is a cow image */
	if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) {
	fprintf(stderr, "%s: could not read header\n", filename);
	goto fail;
	}
	#ifndef _WIN32
	if (be32_to_cpu(cow_header.magic) == COW_MAGIC &&
	be32_to_cpu(cow_header.version) == COW_VERSION) {
	/* cow image found */
	size = cow_header.size;
	#ifndef WORDS_BIGENDIAN
	size = bswap64(size);
	#endif
	bs->total_sectors = size / 512;

	bs->cow_fd = fd;
	bs->fd = -1;
	if (cow_header.backing_file[0] != '\0') {
	if (stat(cow_header.backing_file, &st) != 0) {
	fprintf(stderr, "%s: could not find original disk image '%s'\n", filename, cow_header.backing_file);
	goto fail;
	}
	if (st.st_mtime != be32_to_cpu(cow_header.mtime)) {
	fprintf(stderr, "%s: original raw disk image '%s' does not match saved timestamp\n", filename, cow_header.backing_file);
	goto fail;
	}
	fd = open(cow_header.backing_file, O_RDONLY \| O_LARGEFILE);
	if (fd < 0)
	goto fail;
	bs->fd = fd;
	}
	/* mmap the bitmap */
	bs->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
	bs->cow_bitmap_addr = mmap(get_mmap_addr(bs->cow_bitmap_size),
	bs->cow_bitmap_size,
	PROT_READ \| PROT_WRITE,
	MAP_SHARED, bs->cow_fd, 0);
	if (bs->cow_bitmap_addr == MAP_FAILED)
	goto fail;
	bs->cow_bitmap = bs->cow_bitmap_addr + sizeof(cow_header);
	bs->cow_sectors_offset = (bs->cow_bitmap_size + 511) & ~511;
	snapshot = 0;
	} else
	#endif
	{
	/* standard raw image */
	size = lseek64(fd, 0, SEEK_END);
	bs->total_sectors = size / 512;
	bs->fd = fd;
	}

	#ifndef _WIN32
	if (snapshot) {
	/* create a temporary COW file */
	cow_fd = mkstemp64(template);
	if (cow_fd < 0)
	goto fail;
	bs->cow_fd = cow_fd;
	unlink(template);

	/* just need to allocate bitmap */
	bs->cow_bitmap_size = (bs->total_sectors + 7) >> 3;
	bs->cow_bitmap_addr = mmap(get_mmap_addr(bs->cow_bitmap_size),
	bs->cow_bitmap_size,
	PROT_READ \| PROT_WRITE,
	MAP_PRIVATE \| MAP_ANONYMOUS, -1, 0);
	if (bs->cow_bitmap_addr == MAP_FAILED)
	goto fail;
	bs->cow_bitmap = bs->cow_bitmap_addr;
	bs->cow_sectors_offset = 0;
	}
	#endif

	bs->inserted = 1;

	/* call the change callback */
	if (bs->change_cb)
	bs->change_cb(bs->change_opaque);

	return 0;
	fail:
	bdrv_close(bs);
	return -1;
	}

	void bdrv_close(BlockDriverState *bs)
	{
	if (bs->inserted) {
	#ifndef _WIN32
	/* we unmap the mapping so that it is written to the COW file */
	if (bs->cow_bitmap_addr)
	munmap(bs->cow_bitmap_addr, bs->cow_bitmap_size);
	#endif
	if (bs->cow_fd >= 0)
	close(bs->cow_fd);
	if (bs->fd >= 0)
	close(bs->fd);
	bs->inserted = 0;

	/* call the change callback */
	if (bs->change_cb)
	bs->change_cb(bs->change_opaque);
	}
	}

	void bdrv_delete(BlockDriverState *bs)
	{
	bdrv_close(bs);
	qemu_free(bs);
	}

	static inline void set_bit(uint8_t *bitmap, int64_t bitnum)
	{
	bitmap[bitnum / 8] \|= (1 << (bitnum%8));
	}

	static inline int is_bit_set(const uint8_t *bitmap, int64_t bitnum)
	{
	return !!(bitmap[bitnum / 8] & (1 << (bitnum%8)));
	}


	/* Return true if first block has been changed (ie. current version is
	* in COW file). Set the number of continuous blocks for which that
	* is true. */
	static int is_changed(uint8_t *bitmap,
	int64_t sector_num, int nb_sectors,
	int *num_same)
	{
	int changed;

	if (!bitmap \|\| nb_sectors == 0) {
	*num_same = nb_sectors;
	return 0;
	}

	changed = is_bit_set(bitmap, sector_num);
	for (num_same = 1; num_same < nb_sectors; (*num_same)++) {
	if (is_bit_set(bitmap, sector_num + *num_same) != changed)
	break;
	}

	return changed;
	}

	/* commit COW file into the raw image */
	int bdrv_commit(BlockDriverState *bs)
	{
	int64_t i;
	uint8_t *cow_bitmap;

	if (!bs->inserted)
	return -1;

	if (!bs->cow_bitmap) {
	fprintf(stderr, "Already committed to %s\n", bs->filename);
	return 0;
	}

	if (bs->read_only) {
	fprintf(stderr, "Can't commit to %s: read-only\n", bs->filename);
	return -1;
	}

	cow_bitmap = bs->cow_bitmap;
	for (i = 0; i < bs->total_sectors; i++) {
	if (is_bit_set(cow_bitmap, i)) {
	unsigned char sector[512];
	if (bdrv_read(bs, i, sector, 1) != 0) {
	fprintf(stderr, "Error reading sector %lli: aborting commit\n",
	(long long)i);
	return -1;
	}

	/* Make bdrv_write write to real file for a moment. */
	bs->cow_bitmap = NULL;
	if (bdrv_write(bs, i, sector, 1) != 0) {
	fprintf(stderr, "Error writing sector %lli: aborting commit\n",
	(long long)i);
	bs->cow_bitmap = cow_bitmap;
	return -1;
	}
	bs->cow_bitmap = cow_bitmap;
	}
	}
	fprintf(stderr, "Committed snapshot to %s\n", bs->filename);
	return 0;
	}

	/* return -1 if error */
	int bdrv_read(BlockDriverState *bs, int64_t sector_num,
	uint8_t *buf, int nb_sectors)
	{
	int ret, n, fd;
	int64_t offset;

	if (!bs->inserted)
	return -1;

	while (nb_sectors > 0) {
	if (is_changed(bs->cow_bitmap, sector_num, nb_sectors, &n)) {
	fd = bs->cow_fd;
	offset = bs->cow_sectors_offset;
	} else if (sector_num == 0 && bs->boot_sector_enabled) {
	memcpy(buf, bs->boot_sector_data, 512);
	n = 1;
	goto next;
	} else {
	fd = bs->fd;
	offset = 0;
	}

	if (fd < 0) {
	/* no file, just return empty sectors */
	memset(buf, 0, n * 512);
	} else {
	offset += sector_num * 512;
	lseek64(fd, offset, SEEK_SET);
	ret = read(fd, buf, n * 512);
	if (ret != n * 512) {
	return -1;
	}
	}
	next:
	nb_sectors -= n;
	sector_num += n;
	buf += n * 512;
	}
	return 0;
	}

	/* return -1 if error */
	int bdrv_write(BlockDriverState *bs, int64_t sector_num,
	const uint8_t *buf, int nb_sectors)
	{
	int ret, fd, i;
	int64_t offset, retl;

	if (!bs->inserted)
	return -1;
	if (bs->read_only)
	return -1;

	if (bs->cow_bitmap) {
	fd = bs->cow_fd;
	offset = bs->cow_sectors_offset;
	} else {
	fd = bs->fd;
	offset = 0;
	}

	offset += sector_num * 512;
	retl = lseek64(fd, offset, SEEK_SET);
	if (retl == -1) {
	return -1;
	}
	ret = write(fd, buf, nb_sectors * 512);
	if (ret != nb_sectors * 512) {
	return -1;
	}

	if (bs->cow_bitmap) {
	for (i = 0; i < nb_sectors; i++)
	set_bit(bs->cow_bitmap, sector_num + i);
	}
	return 0;
	}

	void bdrv_get_geometry(BlockDriverState bs, int64_t nb_sectors_ptr)
	{
	*nb_sectors_ptr = bs->total_sectors;
	}

	/* force a given boot sector. */
	void bdrv_set_boot_sector(BlockDriverState bs, const uint8_t data, int size)
	{
	bs->boot_sector_enabled = 1;
	if (size > 512)
	size = 512;
	memcpy(bs->boot_sector_data, data, size);
	memset(bs->boot_sector_data + size, 0, 512 - size);
	}

	void bdrv_set_geometry_hint(BlockDriverState *bs,
	int cyls, int heads, int secs)
	{
	bs->cyls = cyls;
	bs->heads = heads;
	bs->secs = secs;
	}

	void bdrv_set_type_hint(BlockDriverState *bs, int type)
	{
	bs->type = type;
	bs->removable = ((type == BDRV_TYPE_CDROM \|\|
	type == BDRV_TYPE_FLOPPY));
	}

	void bdrv_get_geometry_hint(BlockDriverState *bs,
	int pcyls, int pheads, int *psecs)
	{
	*pcyls = bs->cyls;
	*pheads = bs->heads;
	*psecs = bs->secs;
	}

	int bdrv_get_type_hint(BlockDriverState *bs)
	{
	return bs->type;
	}

	int bdrv_is_removable(BlockDriverState *bs)
	{
	return bs->removable;
	}

	int bdrv_is_read_only(BlockDriverState *bs)
	{
	return bs->read_only;
	}

	int bdrv_is_inserted(BlockDriverState *bs)
	{
	return bs->inserted;
	}

	int bdrv_is_locked(BlockDriverState *bs)
	{
	return bs->locked;
	}

	void bdrv_set_locked(BlockDriverState *bs, int locked)
	{
	bs->locked = locked;
	}

	void bdrv_set_change_cb(BlockDriverState *bs,
	void (change_cb)(void opaque), void *opaque)
	{
	bs->change_cb = change_cb;
	bs->change_opaque = opaque;
	}

	BlockDriverState bdrv_find(const char name)
	{
	BlockDriverState *bs;

	for (bs = bdrv_first; bs != NULL; bs = bs->next) {
	if (!strcmp(name, bs->device_name))
	return bs;
	}
	return NULL;
	}

	void bdrv_info(void)
	{
	BlockDriverState *bs;

	for (bs = bdrv_first; bs != NULL; bs = bs->next) {
	term_printf("%s:", bs->device_name);
	term_printf(" type=");
	switch(bs->type) {
	case BDRV_TYPE_HD:
	term_printf("hd");
	break;
	case BDRV_TYPE_CDROM:
	term_printf("cdrom");
	break;
	case BDRV_TYPE_FLOPPY:
	term_printf("floppy");
	break;
	}
	term_printf(" removable=%d", bs->removable);
	if (bs->removable) {
	term_printf(" locked=%d", bs->locked);
	}
	if (bs->inserted) {
	term_printf(" file=%s", bs->filename);
	term_printf(" ro=%d", bs->read_only);
	} else {
	term_printf(" [not inserted]");
	}
	term_printf("\n");
	}
	}