block/cow.c - qemu - Git at Google

 /*
  * Block driver for the COW format
  *
  * Copyright (c) 2004 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.
  */
 #ifndef _WIN32
 #include "qemu-common.h"
 #include "block_int.h"
 #include "module.h"
 #include <sys/mman.h>

 /**************************************************************/
 /* COW block driver using file system holes */

 /* user mode linux compatible COW file */
 #define COW_MAGIC 0x4f4f4f4d  /* MOOO */
 #define COW_VERSION 2

 struct cow_header_v2 {
     uint32_t magic;
     uint32_t version;
     char backing_file[1024];
     int32_t mtime;
     uint64_t size;
     uint32_t sectorsize;
 };

 typedef struct BDRVCowState {
     int fd;
     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;
     int64_t cow_sectors_offset;
 } BDRVCowState;

 static int cow_probe(const uint8_t *buf, int buf_size, const char *filename)
 {
     const struct cow_header_v2 *cow_header = (const void *)buf;

     if (buf_size >= sizeof(struct cow_header_v2) &&
         be32_to_cpu(cow_header->magic) == COW_MAGIC &&
         be32_to_cpu(cow_header->version) == COW_VERSION)
         return 100;
     else
         return 0;
 }

 static int cow_open(BlockDriverState *bs, const char *filename, int flags)
 {
     BDRVCowState *s = bs->opaque;
     int fd;
     struct cow_header_v2 cow_header;
     int64_t size;

     fd = open(filename, O_RDWR | O_BINARY | O_LARGEFILE);
     if (fd < 0) {
         fd = open(filename, O_RDONLY | O_BINARY | O_LARGEFILE);
         if (fd < 0)
             return -1;
     }
     s->fd = fd;
     /* see if it is a cow image */
     if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) {
         goto fail;
     }

     if (be32_to_cpu(cow_header.magic) != COW_MAGIC ||
         be32_to_cpu(cow_header.version) != COW_VERSION) {
         goto fail;
     }

     /* cow image found */
     size = be64_to_cpu(cow_header.size);
     bs->total_sectors = size / 512;

     pstrcpy(bs->backing_file, sizeof(bs->backing_file),
             cow_header.backing_file);

     /* mmap the bitmap */
     s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
     s->cow_bitmap_addr = (void *)mmap(get_mmap_addr(s->cow_bitmap_size),
                                       s->cow_bitmap_size,
                                       PROT_READ | PROT_WRITE,
                                       MAP_SHARED, s->fd, 0);
     if (s->cow_bitmap_addr == MAP_FAILED)
         goto fail;
     s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header);
     s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511;
     return 0;
  fail:
     close(fd);
     return -1;
 }

 static inline void cow_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 inline 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;
 }

 static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num,
                             int nb_sectors, int *pnum)
 {
     BDRVCowState *s = bs->opaque;
     return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum);
 }

 static int cow_read(BlockDriverState *bs, int64_t sector_num,
                     uint8_t *buf, int nb_sectors)
 {
     BDRVCowState *s = bs->opaque;
     int ret, n;

     while (nb_sectors > 0) {
         if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
             lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
             ret = read(s->fd, buf, n * 512);
             if (ret != n * 512)
                 return -1;
         } else {
             if (bs->backing_hd) {
                 /* read from the base image */
                 ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
                 if (ret < 0)
                     return -1;
             } else {
             memset(buf, 0, n * 512);
         }
         }
         nb_sectors -= n;
         sector_num += n;
         buf += n * 512;
     }
     return 0;
 }

 static int cow_write(BlockDriverState *bs, int64_t sector_num,
                      const uint8_t *buf, int nb_sectors)
 {
     BDRVCowState *s = bs->opaque;
     int ret, i;

     lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
     ret = write(s->fd, buf, nb_sectors * 512);
     if (ret != nb_sectors * 512)
         return -1;
     for (i = 0; i < nb_sectors; i++)
         cow_set_bit(s->cow_bitmap, sector_num + i);
     return 0;
 }

 static void cow_close(BlockDriverState *bs)
 {
     BDRVCowState *s = bs->opaque;
     munmap((void *)s->cow_bitmap_addr, s->cow_bitmap_size);
     close(s->fd);
 }

 static int cow_create(const char *filename, QEMUOptionParameter *options)
 {
     int fd, cow_fd;
     struct cow_header_v2 cow_header;
     struct stat st;
     int64_t image_sectors = 0;
     const char *image_filename = NULL;
     int ret;

     /* Read out options */
     while (options && options->name) {
         if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
             image_sectors = options->value.n / 512;
         } else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
             image_filename = options->value.s;
         }
         options++;
     }

     cow_fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
               0644);
     if (cow_fd < 0)
         return -errno;
     memset(&cow_header, 0, sizeof(cow_header));
     cow_header.magic = cpu_to_be32(COW_MAGIC);
     cow_header.version = cpu_to_be32(COW_VERSION);
     if (image_filename) {
         /* Note: if no file, we put a dummy mtime */
         cow_header.mtime = cpu_to_be32(0);

         fd = open(image_filename, O_RDONLY | O_BINARY);
         if (fd < 0) {
             close(cow_fd);
             goto mtime_fail;
         }
         if (fstat(fd, &st) != 0) {
             close(fd);
             goto mtime_fail;
         }
         close(fd);
         cow_header.mtime = cpu_to_be32(st.st_mtime);
     mtime_fail:
         pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
                 image_filename);
     }
     cow_header.sectorsize = cpu_to_be32(512);
     cow_header.size = cpu_to_be64(image_sectors * 512);
     ret = qemu_write_full(cow_fd, &cow_header, sizeof(cow_header));
     if (ret != sizeof(cow_header)) {
         ret = -errno;
         goto exit;
     }

     /* resize to include at least all the bitmap */
     ret = ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
     if (ret) {
         ret = -errno;
         goto exit;
     }

 exit:
     close(cow_fd);
     return ret;
 }

 static void cow_flush(BlockDriverState *bs)
 {
     BDRVCowState *s = bs->opaque;
     qemu_fdatasync(s->fd);
 }

 static QEMUOptionParameter cow_create_options[] = {
     {
         .name = BLOCK_OPT_SIZE,
         .type = OPT_SIZE,
         .help = "Virtual disk size"
     },
     {
         .name = BLOCK_OPT_BACKING_FILE,
         .type = OPT_STRING,
         .help = "File name of a base image"
     },
     { NULL }
 };

 static BlockDriver bdrv_cow = {
     .format_name	= "cow",
     .instance_size	= sizeof(BDRVCowState),
     .bdrv_probe		= cow_probe,
     .bdrv_open		= cow_open,
     .bdrv_read		= cow_read,
     .bdrv_write		= cow_write,
     .bdrv_close		= cow_close,
     .bdrv_create	= cow_create,
     .bdrv_flush		= cow_flush,
     .bdrv_is_allocated	= cow_is_allocated,

     .create_options = cow_create_options,
 };

 static void bdrv_cow_init(void)
 {
     bdrv_register(&bdrv_cow);
 }

 block_init(bdrv_cow_init);
 #endif
	/*
	* Block driver for the COW format
	*
	* Copyright (c) 2004 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.
	*/
	#ifndef _WIN32
	#include "qemu-common.h"
	#include "block_int.h"
	#include "module.h"
	#include <sys/mman.h>

	/**************************************************************/
	/* COW block driver using file system holes */

	/* user mode linux compatible COW file */
	#define COW_MAGIC 0x4f4f4f4d /* MOOO */
	#define COW_VERSION 2

	struct cow_header_v2 {
	uint32_t magic;
	uint32_t version;
	char backing_file[1024];
	int32_t mtime;
	uint64_t size;
	uint32_t sectorsize;
	};

	typedef struct BDRVCowState {
	int fd;
	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;
	int64_t cow_sectors_offset;
	} BDRVCowState;

	static int cow_probe(const uint8_t buf, int buf_size, const char filename)
	{
	const struct cow_header_v2 cow_header = (const void )buf;

	if (buf_size >= sizeof(struct cow_header_v2) &&
	be32_to_cpu(cow_header->magic) == COW_MAGIC &&
	be32_to_cpu(cow_header->version) == COW_VERSION)
	return 100;
	else
	return 0;
	}

	static int cow_open(BlockDriverState bs, const char filename, int flags)
	{
	BDRVCowState *s = bs->opaque;
	int fd;
	struct cow_header_v2 cow_header;
	int64_t size;

	fd = open(filename, O_RDWR \| O_BINARY \| O_LARGEFILE);
	if (fd < 0) {
	fd = open(filename, O_RDONLY \| O_BINARY \| O_LARGEFILE);
	if (fd < 0)
	return -1;
	}
	s->fd = fd;
	/* see if it is a cow image */
	if (read(fd, &cow_header, sizeof(cow_header)) != sizeof(cow_header)) {
	goto fail;
	}

	if (be32_to_cpu(cow_header.magic) != COW_MAGIC \|\|
	be32_to_cpu(cow_header.version) != COW_VERSION) {
	goto fail;
	}

	/* cow image found */
	size = be64_to_cpu(cow_header.size);
	bs->total_sectors = size / 512;

	pstrcpy(bs->backing_file, sizeof(bs->backing_file),
	cow_header.backing_file);

	/* mmap the bitmap */
	s->cow_bitmap_size = ((bs->total_sectors + 7) >> 3) + sizeof(cow_header);
	s->cow_bitmap_addr = (void *)mmap(get_mmap_addr(s->cow_bitmap_size),
	s->cow_bitmap_size,
	PROT_READ \| PROT_WRITE,
	MAP_SHARED, s->fd, 0);
	if (s->cow_bitmap_addr == MAP_FAILED)
	goto fail;
	s->cow_bitmap = s->cow_bitmap_addr + sizeof(cow_header);
	s->cow_sectors_offset = (s->cow_bitmap_size + 511) & ~511;
	return 0;
	fail:
	close(fd);
	return -1;
	}

	static inline void cow_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 inline 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;
	}

	static int cow_is_allocated(BlockDriverState *bs, int64_t sector_num,
	int nb_sectors, int *pnum)
	{
	BDRVCowState *s = bs->opaque;
	return is_changed(s->cow_bitmap, sector_num, nb_sectors, pnum);
	}

	static int cow_read(BlockDriverState *bs, int64_t sector_num,
	uint8_t *buf, int nb_sectors)
	{
	BDRVCowState *s = bs->opaque;
	int ret, n;

	while (nb_sectors > 0) {
	if (is_changed(s->cow_bitmap, sector_num, nb_sectors, &n)) {
	lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
	ret = read(s->fd, buf, n * 512);
	if (ret != n * 512)
	return -1;
	} else {
	if (bs->backing_hd) {
	/* read from the base image */
	ret = bdrv_read(bs->backing_hd, sector_num, buf, n);
	if (ret < 0)
	return -1;
	} else {
	memset(buf, 0, n * 512);
	}
	}
	nb_sectors -= n;
	sector_num += n;
	buf += n * 512;
	}
	return 0;
	}

	static int cow_write(BlockDriverState *bs, int64_t sector_num,
	const uint8_t *buf, int nb_sectors)
	{
	BDRVCowState *s = bs->opaque;
	int ret, i;

	lseek(s->fd, s->cow_sectors_offset + sector_num * 512, SEEK_SET);
	ret = write(s->fd, buf, nb_sectors * 512);
	if (ret != nb_sectors * 512)
	return -1;
	for (i = 0; i < nb_sectors; i++)
	cow_set_bit(s->cow_bitmap, sector_num + i);
	return 0;
	}

	static void cow_close(BlockDriverState *bs)
	{
	BDRVCowState *s = bs->opaque;
	munmap((void *)s->cow_bitmap_addr, s->cow_bitmap_size);
	close(s->fd);
	}

	static int cow_create(const char filename, QEMUOptionParameter options)
	{
	int fd, cow_fd;
	struct cow_header_v2 cow_header;
	struct stat st;
	int64_t image_sectors = 0;
	const char *image_filename = NULL;
	int ret;

	/* Read out options */
	while (options && options->name) {
	if (!strcmp(options->name, BLOCK_OPT_SIZE)) {
	image_sectors = options->value.n / 512;
	} else if (!strcmp(options->name, BLOCK_OPT_BACKING_FILE)) {
	image_filename = options->value.s;
	}
	options++;
	}

	cow_fd = open(filename, O_WRONLY \| O_CREAT \| O_TRUNC \| O_BINARY,
	0644);
	if (cow_fd < 0)
	return -errno;
	memset(&cow_header, 0, sizeof(cow_header));
	cow_header.magic = cpu_to_be32(COW_MAGIC);
	cow_header.version = cpu_to_be32(COW_VERSION);
	if (image_filename) {
	/* Note: if no file, we put a dummy mtime */
	cow_header.mtime = cpu_to_be32(0);

	fd = open(image_filename, O_RDONLY \| O_BINARY);
	if (fd < 0) {
	close(cow_fd);
	goto mtime_fail;
	}
	if (fstat(fd, &st) != 0) {
	close(fd);
	goto mtime_fail;
	}
	close(fd);
	cow_header.mtime = cpu_to_be32(st.st_mtime);
	mtime_fail:
	pstrcpy(cow_header.backing_file, sizeof(cow_header.backing_file),
	image_filename);
	}
	cow_header.sectorsize = cpu_to_be32(512);
	cow_header.size = cpu_to_be64(image_sectors * 512);
	ret = qemu_write_full(cow_fd, &cow_header, sizeof(cow_header));
	if (ret != sizeof(cow_header)) {
	ret = -errno;
	goto exit;
	}

	/* resize to include at least all the bitmap */
	ret = ftruncate(cow_fd, sizeof(cow_header) + ((image_sectors + 7) >> 3));
	if (ret) {
	ret = -errno;
	goto exit;
	}

	exit:
	close(cow_fd);
	return ret;
	}

	static void cow_flush(BlockDriverState *bs)
	{
	BDRVCowState *s = bs->opaque;
	qemu_fdatasync(s->fd);
	}

	static QEMUOptionParameter cow_create_options[] = {
	{
	.name = BLOCK_OPT_SIZE,
	.type = OPT_SIZE,
	.help = "Virtual disk size"
	},
	{
	.name = BLOCK_OPT_BACKING_FILE,
	.type = OPT_STRING,
	.help = "File name of a base image"
	},
	{ NULL }
	};

	static BlockDriver bdrv_cow = {
	.format_name = "cow",
	.instance_size = sizeof(BDRVCowState),
	.bdrv_probe = cow_probe,
	.bdrv_open = cow_open,
	.bdrv_read = cow_read,
	.bdrv_write = cow_write,
	.bdrv_close = cow_close,
	.bdrv_create = cow_create,
	.bdrv_flush = cow_flush,
	.bdrv_is_allocated = cow_is_allocated,

	.create_options = cow_create_options,
	};

	static void bdrv_cow_init(void)
	{
	bdrv_register(&bdrv_cow);
	}

	block_init(bdrv_cow_init);
	#endif