This patch allows an empty filename to be passed as the new base image name for qemu-img rebase to mean base the image on no backing file (i.e. independent of any backing file). According to Eric Blake, qemu-img rebase already supports this when '-u' is used; this adds support when -u is not used.
Signed-off-by: Alex Bligh <a...@alex.org.uk> --- qemu-img.c | 29 +++++++++++++++++++---------- qemu-img.texi | 4 +++- 2 files changed, 22 insertions(+), 11 deletions(-) Also obtainable from: https://github.com/abligh/qemu.git Commit at: https://github.com/abligh/qemu/commit/982ec105018f9901619663642de9d0a5de86799d diff --git a/qemu-img.c b/qemu-img.c index f17f187..2816f37 100644 --- a/qemu-img.c +++ b/qemu-img.c @@ -1558,13 +1558,15 @@ static int img_rebase(int argc, char **argv) error_report("Could not open old backing file '%s'", backing_name); goto out; } - - bs_new_backing = bdrv_new("new_backing"); - ret = bdrv_open(bs_new_backing, out_baseimg, BDRV_O_FLAGS, + if (out_baseimg[0]) { + bs_new_backing = bdrv_new("new_backing"); + ret = bdrv_open(bs_new_backing, out_baseimg, BDRV_O_FLAGS, new_backing_drv); - if (ret) { - error_report("Could not open new backing file '%s'", out_baseimg); - goto out; + if (ret) { + error_report("Could not open new backing file '%s'", + out_baseimg); + goto out; + } } } @@ -1580,7 +1582,7 @@ static int img_rebase(int argc, char **argv) if (!unsafe) { uint64_t num_sectors; uint64_t old_backing_num_sectors; - uint64_t new_backing_num_sectors; + uint64_t new_backing_num_sectors = 0; uint64_t sector; int n; uint8_t * buf_old; @@ -1592,7 +1594,9 @@ static int img_rebase(int argc, char **argv) bdrv_get_geometry(bs, &num_sectors); bdrv_get_geometry(bs_old_backing, &old_backing_num_sectors); - bdrv_get_geometry(bs_new_backing, &new_backing_num_sectors); + if (bs_new_backing) { + bdrv_get_geometry(bs_new_backing, &new_backing_num_sectors); + } local_progress = (float)100 / (num_sectors / MIN(num_sectors, IO_BUF_SIZE / 512)); @@ -1629,7 +1633,7 @@ static int img_rebase(int argc, char **argv) } } - if (sector >= new_backing_num_sectors) { + if (sector >= new_backing_num_sectors || !bs_new_backing) { memset(buf_new, 0, n * BDRV_SECTOR_SIZE); } else { if (sector + n > new_backing_num_sectors) { @@ -1675,7 +1679,12 @@ static int img_rebase(int argc, char **argv) * 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 (bs_new_backing) { + ret = bdrv_change_backing_file(bs, out_baseimg, out_basefmt); + } else { + ret = bdrv_change_backing_file(bs, NULL, NULL); + } + if (ret == -ENOSPC) { error_report("Could not change the backing file to '%s': No " "space left in the file header", out_baseimg); diff --git a/qemu-img.texi b/qemu-img.texi index 8b05f2c..42ec392 100644 --- a/qemu-img.texi +++ b/qemu-img.texi @@ -148,7 +148,9 @@ Changes the backing file of an image. Only the formats @code{qcow2} and The backing file is changed to @var{backing_file} and (if the image format of @var{filename} supports this) the backing file format is changed to -@var{backing_fmt}. +@var{backing_fmt}. If @var{backing_file} is specified as ``'' (the empty +string), then the image is rebased onto no backing file (i.e. it will exist +independently of any backing file). There are two different modes in which @code{rebase} can operate: @table @option -- 1.7.4.1
