" name=value format. Use -o ? for an overview of the options supported by the\n"
" used format\n"
" '-c' indicates that target image must be compressed (qcow format only)\n"
+ " '-u' enables unsafe rebasing. It is assumed that old and new backing file\n"
+ " match exactly. The image doesn't need a working backing file before\n"
+ " rebasing in this case (useful for renaming the backing file)\n"
" '-h' with or without a command shows this help and lists the supported formats\n"
"\n"
"Parameters to snapshot subcommand:\n"
return v;
}
+/*
+ * Compares two buffers sector by sector. Returns 0 if the first sector of both
+ * buffers matches, non-zero otherwise.
+ *
+ * pnum is set to the number of sectors (including and immediately following
+ * the first one) that are known to have the same comparison result
+ */
+static int compare_sectors(const uint8_t *buf1, const uint8_t *buf2, int n,
+ int *pnum)
+{
+ int res, i;
+
+ if (n <= 0) {
+ *pnum = 0;
+ return 0;
+ }
+
+ res = !!memcmp(buf1, buf2, 512);
+ for(i = 1; i < n; i++) {
+ buf1 += 512;
+ buf2 += 512;
+
+ if (!!memcmp(buf1, buf2, 512) != res) {
+ break;
+ }
+ }
+
+ *pnum = i;
+ return res;
+}
+
#define IO_BUF_SIZE (2 * 1024 * 1024)
static int img_convert(int argc, char **argv)
return 0;
}
+static int img_rebase(int argc, char **argv)
+{
+ BlockDriverState *bs, *bs_old_backing, *bs_new_backing;
+ BlockDriver *old_backing_drv, *new_backing_drv;
+ char *filename;
+ const char *out_basefmt, *out_baseimg;
+ int c, flags, ret;
+ int unsafe = 0;
+
+ /* Parse commandline parameters */
+ out_baseimg = NULL;
+ out_basefmt = NULL;
+
+ for(;;) {
+ c = getopt(argc, argv, "uhF:b:");
+ if (c == -1)
+ break;
+ switch(c) {
+ case 'h':
+ help();
+ return 0;
+ case 'F':
+ out_basefmt = optarg;
+ break;
+ case 'b':
+ out_baseimg = optarg;
+ break;
+ case 'u':
+ unsafe = 1;
+ break;
+ }
+ }
+
+ if ((optind >= argc) || !out_baseimg)
+ help();
+ filename = argv[optind++];
+
+ /*
+ * Open the images.
+ *
+ * Ignore the old backing file for unsafe rebase in case we want to correct
+ * the reference to a renamed or moved backing file.
+ */
+ bs = bdrv_new("");
+ if (!bs)
+ error("Not enough memory");
+
+ flags = BRDV_O_FLAGS | (unsafe ? BDRV_O_NO_BACKING : 0);
+ if (bdrv_open2(bs, filename, flags, NULL) < 0) {
+ error("Could not open '%s'", filename);
+ }
+
+ /* Find the right drivers for the backing files */
+ old_backing_drv = NULL;
+ new_backing_drv = NULL;
+
+ if (!unsafe && bs->backing_format[0] != '\0') {
+ old_backing_drv = bdrv_find_format(bs->backing_format);
+ if (old_backing_drv == NULL) {
+ error("Invalid format name: '%s'", bs->backing_format);
+ }
+ }
+
+ if (out_basefmt != NULL) {
+ new_backing_drv = bdrv_find_format(out_basefmt);
+ if (new_backing_drv == NULL) {
+ error("Invalid format name: '%s'", out_basefmt);
+ }
+ }
+
+ /* For safe rebasing we need to compare old and new backing file */
+ if (unsafe) {
+ /* Make the compiler happy */
+ bs_old_backing = NULL;
+ bs_new_backing = NULL;
+ } else {
+ char backing_name[1024];
+
+ bs_old_backing = bdrv_new("old_backing");
+ bdrv_get_backing_filename(bs, backing_name, sizeof(backing_name));
+ if (bdrv_open2(bs_old_backing, backing_name, BRDV_O_FLAGS,
+ old_backing_drv))
+ {
+ error("Could not open old backing file '%s'", backing_name);
+ return -1;
+ }
+
+ bs_new_backing = bdrv_new("new_backing");
+ if (bdrv_open2(bs_new_backing, out_baseimg, BRDV_O_FLAGS,
+ new_backing_drv))
+ {
+ error("Could not open new backing file '%s'", backing_name);
+ return -1;
+ }
+ }
+
+ /*
+ * Check each unallocated cluster in the COW file. If it is unallocated,
+ * accesses go to the backing file. We must therefore compare this cluster
+ * in the old and new backing file, and if they differ we need to copy it
+ * from the old backing file into the COW file.
+ *
+ * If qemu-img crashes during this step, no harm is done. The content of
+ * the image is the same as the original one at any time.
+ */
+ if (!unsafe) {
+ uint64_t num_sectors;
+ uint64_t sector;
+ int n, n1;
+ uint8_t buf_old[IO_BUF_SIZE];
+ uint8_t buf_new[IO_BUF_SIZE];
+
+ bdrv_get_geometry(bs, &num_sectors);
+
+ for (sector = 0; sector < num_sectors; sector += n) {
+
+ /* How many sectors can we handle with the next read? */
+ if (sector + (IO_BUF_SIZE / 512) <= num_sectors) {
+ n = (IO_BUF_SIZE / 512);
+ } else {
+ n = num_sectors - sector;
+ }
+
+ /* If the cluster is allocated, we don't need to take action */
+ if (bdrv_is_allocated(bs, sector, n, &n1)) {
+ n = n1;
+ continue;
+ }
+
+ /* Read old and new backing file */
+ if (bdrv_read(bs_old_backing, sector, buf_old, n) < 0) {
+ error("error while reading from old backing file");
+ }
+ if (bdrv_read(bs_new_backing, sector, buf_new, n) < 0) {
+ error("error while reading from new backing file");
+ }
+
+ /* If they differ, we need to write to the COW file */
+ uint64_t written = 0;
+
+ while (written < n) {
+ int pnum;
+
+ if (compare_sectors(buf_old + written * 512,
+ buf_new + written * 512, n, &pnum))
+ {
+ ret = bdrv_write(bs, sector + written,
+ buf_old + written * 512, pnum);
+ if (ret < 0) {
+ error("Error while writing to COW image: %s",
+ strerror(-ret));
+ }
+ }
+
+ written += pnum;
+ }
+ }
+ }
+
+ /*
+ * Change the backing file. All clusters that are different from the old
+ * backing file are overwritten in the COW file now, so the visible content
+ * doesn't change when we switch the backing file.
+ */
+ ret = bdrv_change_backing_file(bs, out_baseimg, out_basefmt);
+ if (ret == -ENOSPC) {
+ error("Could not change the backing file to '%s': No space left in "
+ "the file header", out_baseimg);
+ } else if (ret < 0) {
+ error("Could not change the backing file to '%s': %s",
+ out_baseimg, strerror(-ret));
+ }
+
+ /*
+ * TODO At this point it is possible to check if any clusters that are
+ * allocated in the COW file are the same in the backing file. If so, they
+ * could be dropped from the COW file. Don't do this before switching the
+ * backing file, in case of a crash this would lead to corruption.
+ */
+
+ /* Cleanup */
+ if (!unsafe) {
+ bdrv_delete(bs_old_backing);
+ bdrv_delete(bs_new_backing);
+ }
+
+ bdrv_delete(bs);
+
+ return 0;
+}
+
static const img_cmd_t img_cmds[] = {
#define DEF(option, callback, arg_string) \
{ option, callback },
projects / sdk / emulator / qemu.git / commitdiff