From: "Richard W.M. Jones" <rjo...@redhat.com>
This produces a qcow2 file which is the different between
two disk images. ie, if:
original.img - is a disk image (in any format)
modified.img - is a modified version of original.img
then:
qemu-img diff -b original.img modified.img diff.qcow2
creates 'diff.qcow2' which contains just the differences. Note that
'diff.qcow2' has 'original.img' set as the backing file.
Signed-off-by: Richard W.M. Jones <rjo...@redhat.com>
Cc: Matthew Booth <mbo...@redhat.com>
Cc: Pablo Iranzo Gómez <pablo.ira...@redhat.com>
Cc: Tomas Von Veschler <tvv...@redhat.com>
---
qemu-img-cmds.hx | 6 +++
qemu-img.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
qemu-img.texi | 17 +++++++
3 files changed, 173 insertions(+)
diff --git a/qemu-img-cmds.hx b/qemu-img-cmds.hx
index 49dce7c..01a9246 100644
--- a/qemu-img-cmds.hx
+++ b/qemu-img-cmds.hx
@@ -33,6 +33,12 @@ STEXI
@item convert [-c] [-p] [-f @var{fmt}] [-t @var{cache}] [-O @var{output_fmt}]
[-o @var{options}] [-s @var{snapshot_name}] [-S @var{sparse_size}]
@var{filename} [@var{filename2} [...]] @var{output_filename}
ETEXI
+DEF("diff", img_diff,
+ "diff [-f fmt] [-F backing_fmt] [-O output_fmt] -b backing_file filename
output_filename")
+STEXI
+@item rebase [-f @var{fmt}] [-F @var{backing_fmt}] [-O @var{output_fmt}] -b
@var{backing_file} @var{filename} @var{output_filename}
+ETEXI
+
DEF("info", img_info,
"info [-f fmt] filename")
STEXI
diff --git a/qemu-img.c b/qemu-img.c
index c8a70ff..6e3fe2a 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1533,6 +1533,156 @@ out:
return 0;
}
+static int img_diff(int argc, char **argv)
+{
+ /* qemu-img diff -b original modified out */
+ BlockDriverState *bs_original, *bs_modified, *bs_out;
+ const char *fmt_original, *original,
+ *fmt_modified, *modified,
+ *fmt_out, *out;
+ int c, ret = 0;
+ uint64_t num_sectors, modified_num_sectors;
+ uint64_t sector;
+ int n;
+ uint8_t *buf_original;
+ uint8_t *buf_modified;
+
+ /* Parse commandline parameters */
+ fmt_original = NULL;
+ fmt_modified = NULL;
+ fmt_out = NULL;
+ original = NULL;
+ for(;;) {
+ c = getopt(argc, argv, "hf:F:b:O:");
+ if (c == -1) {
+ break;
+ }
+ switch(c) {
+ case '?':
+ case 'h':
+ help();
+ return 0;
+ case 'f':
+ fmt_modified = optarg;
+ break;
+ case 'F':
+ fmt_original = optarg;
+ break;
+ case 'b':
+ original = optarg;
+ break;
+ case 'O':
+ fmt_out = optarg;
+ break;
+ }
+ }
+
+ if (original == NULL) {
+ error_report("The -b (backing filename) option must be supplied");
+ return 1;
+ }
+
+ if (argc - optind != 2) {
+ error_report("The input and output filenames must be supplied");
+ return 1;
+ }
+ modified = argv[optind++];
+ out = argv[optind++];
+
+ /* Open the input images. */
+ bs_original = bdrv_new_open(original, fmt_original, BDRV_O_FLAGS);
+ if (!bs_original) {
+ return 1;
+ }
+
+ bs_modified = bdrv_new_open(modified, fmt_modified, BDRV_O_FLAGS);
+ if (!bs_modified) {
+ return 1;
+ }
+
+ bdrv_get_geometry(bs_original, &num_sectors);
+ bdrv_get_geometry(bs_modified, &modified_num_sectors);
+ if (num_sectors != modified_num_sectors) {
+ error_report("Number of sectors in backing and source must be the
same");
+ goto out2;
+ }
+
+ /* Output image. */
+ if (fmt_out == NULL || fmt_out[0] == '\0') {
+ fmt_out = "qcow2";
+ }
+ ret = bdrv_img_create(out, fmt_out,
+ /* original file becomes the new backing file */
+ original, fmt_original,
+ NULL, num_sectors * BDRV_SECTOR_SIZE, BDRV_O_FLAGS);
+ if (ret != 0) {
+ goto out2;
+ }
+ bs_out = bdrv_new_open(out, fmt_out, BDRV_O_RDWR);
+
+ buf_original = qemu_blockalign(bs_original, IO_BUF_SIZE);
+ buf_modified = qemu_blockalign(bs_modified, IO_BUF_SIZE);
+
+ for (sector = 0; sector < num_sectors; sector += n) {
+ /* How many sectors can we handle with the next read? */
+ if (sector + (IO_BUF_SIZE / BDRV_SECTOR_SIZE) <= num_sectors) {
+ n = IO_BUF_SIZE / BDRV_SECTOR_SIZE;
+ } else {
+ n = num_sectors - sector;
+ }
+
+ /* Read input files and compare. */
+ ret = bdrv_read(bs_original, sector, buf_original, n);
+ if (ret < 0) {
+ error_report("error while reading from backing file");
+ goto out;
+ }
+
+ ret = bdrv_read(bs_modified, sector, buf_modified, n);
+ if (ret < 0) {
+ error_report("error while reading from input file");
+ goto out;
+ }
+
+ /* If they differ, we need to write to the differences file. */
+ uint64_t written = 0;
+
+ while (written < n) {
+ int pnum;
+
+ if (compare_sectors(buf_original + written * BDRV_SECTOR_SIZE,
+ buf_modified + written * BDRV_SECTOR_SIZE,
+ n - written, &pnum)) {
+ ret = bdrv_write(bs_out, sector + written,
+ buf_modified + written * BDRV_SECTOR_SIZE,
+ pnum);
+ if (ret < 0) {
+ error_report("Error while writing to output file: %s",
+ strerror(-ret));
+ goto out;
+ }
+ }
+
+ written += pnum;
+ }
+ }
+
+ qemu_vfree(buf_original);
+ qemu_vfree(buf_modified);
+
+ out:
+ /* Cleanup */
+ bdrv_delete(bs_out);
+ out2:
+ bdrv_delete(bs_original);
+ bdrv_delete(bs_modified);
+
+ if (ret) {
+ return 1;
+ }
+ return 0;
+}
+
static int img_resize(int argc, char **argv)
{
int c, ret, relative;
diff --git a/qemu-img.texi b/qemu-img.texi
index b2ca3a5..e1a123b 100644
--- a/qemu-img.texi
+++ b/qemu-img.texi
@@ -114,6 +114,23 @@ created as a copy on write image of the specified base
image; the
@var{backing_file} should have the same content as the input's base image,
however the path, image format, etc may differ.
+@item diff [-f @var{fmt}] [-F @var{backing_fmt}] [-O @var{output_fmt}] -b
@var{backing_file} @var{filename} @var{output_filename}
+
+Create a new file (@var{output_filename}) which contains the
+differences between @var{backing_file} and @var{filename}.
+
+The @var{backing_file} and @var{filename} must have the same
+virtual disk size, but may be in different formats.
+
+@var{output_file} will have @var{backing_file} set as its backing
+file. The format of @var{output_file} must be one that supports
+backing files (currently @code{qcow2} is the default and only
+permitted output format).
+
+Typical usage is:
+
+@code{qemu-img diff -b original.img modified.img diff.qcow2}
+
@item info [-f @var{fmt}] @var{filename}
Give information about the disk image @var{filename}. Use it in
--
1.7.10
