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authorMax Reitz <mreitz@redhat.com>2018-08-01 20:34:11 +0200
committerKevin Wolf <kwolf@redhat.com>2020-09-07 12:31:31 +0200
commit0b877d09df4557900149384d60be0e9c3d309105 (patch)
tree2832de2aa2fc1df6813921c57c9666a8e09562ef /block.c
parent549ec0d9783e1a94e502e677fe0ce4a90c0bd7df (diff)
block: Leave BDS.backing_{file,format} constant
Parts of the block layer treat BDS.backing_file as if it were whatever the image header says (i.e., if it is a relative path, it is relative to the overlay), other parts treat it like a cache for bs->backing->bs->filename (relative paths are relative to the CWD). Considering bs->backing->bs->filename exists, let us make it mean the former. Among other things, this now allows the user to specify a base when using qemu-img to commit an image file in a directory that is not the CWD (assuming, everything uses relative filenames). Before this patch: $ ./qemu-img create -f qcow2 foo/bot.qcow2 1M $ ./qemu-img create -f qcow2 -b bot.qcow2 foo/mid.qcow2 $ ./qemu-img create -f qcow2 -b mid.qcow2 foo/top.qcow2 $ ./qemu-img commit -b mid.qcow2 foo/top.qcow2 qemu-img: Did not find 'mid.qcow2' in the backing chain of 'foo/top.qcow2' $ ./qemu-img commit -b foo/mid.qcow2 foo/top.qcow2 qemu-img: Did not find 'foo/mid.qcow2' in the backing chain of 'foo/top.qcow2' $ ./qemu-img commit -b $PWD/foo/mid.qcow2 foo/top.qcow2 qemu-img: Did not find '[...]/foo/mid.qcow2' in the backing chain of 'foo/top.qcow2' After this patch: $ ./qemu-img commit -b mid.qcow2 foo/top.qcow2 Image committed. $ ./qemu-img commit -b foo/mid.qcow2 foo/top.qcow2 qemu-img: Did not find 'foo/mid.qcow2' in the backing chain of 'foo/top.qcow2' $ ./qemu-img commit -b $PWD/foo/mid.qcow2 foo/top.qcow2 Image committed. With this change, bdrv_find_backing_image() must look at whether the user has overridden a BDS's backing file. If so, it can no longer use bs->backing_file, but must instead compare the given filename against the backing node's filename directly. Note that this changes the QAPI output for a node's backing_file. We had very inconsistent output there (sometimes what the image header said, sometimes the actual filename of the backing image). This inconsistent output was effectively useless, so we have to decide one way or the other. Considering that bs->backing_file usually at runtime contained the path to the image relative to qemu's CWD (or absolute), this patch changes QAPI's backing_file to always report the bs->backing->bs->filename from now on. If you want to receive the image header information, you have to refer to full-backing-filename. This necessitates a change to iotest 228. The interesting information it really wanted is the image header, and it can get that now, but it has to use full-backing-filename instead of backing_file. Because of this patch's changes to bs->backing_file's behavior, we also need some reference output changes. Along with the changes to bs->backing_file, stop updating BDS.backing_format in bdrv_backing_attach() as well. This way, ImageInfo's backing-filename and backing-filename-format fields will represent what the image header says and nothing else. iotest 245 changes in behavior: With the backing node no longer overriding the parent node's backing_file string, you can now omit the @backing option when reopening a node with neither a default nor a current backing file even if it used to have a backing node at some point. 273 also changes: The base image is opened without a format layer, so ImageInfo.backing-filename-format used to report "file" for the base image's overlay after blockdev-snapshot. However, the image header never says "file" anywhere, so it now reports $IMGFMT. Signed-off-by: Max Reitz <mreitz@redhat.com>
Diffstat (limited to 'block.c')
-rw-r--r--block.c35
1 files changed, 27 insertions, 8 deletions
diff --git a/block.c b/block.c
index 63c7d9b1a7..9538af4884 100644
--- a/block.c
+++ b/block.c
@@ -1155,10 +1155,6 @@ static void bdrv_backing_attach(BdrvChild *c)
bdrv_refresh_filename(backing_hd);
parent->open_flags &= ~BDRV_O_NO_BACKING;
- pstrcpy(parent->backing_file, sizeof(parent->backing_file),
- backing_hd->filename);
- pstrcpy(parent->backing_format, sizeof(parent->backing_format),
- backing_hd->drv ? backing_hd->drv->format_name : "");
bdrv_op_block_all(backing_hd, parent->backing_blocker);
/* Otherwise we won't be able to commit or stream */
@@ -5673,6 +5669,7 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
char *backing_file_full = NULL;
char *filename_tmp = NULL;
int is_protocol = 0;
+ bool filenames_refreshed = false;
BlockDriverState *curr_bs = NULL;
BlockDriverState *retval = NULL;
BlockDriverState *bs_below;
@@ -5698,9 +5695,31 @@ BlockDriverState *bdrv_find_backing_image(BlockDriverState *bs,
{
bs_below = bdrv_backing_chain_next(curr_bs);
- /* If either of the filename paths is actually a protocol, then
- * compare unmodified paths; otherwise make paths relative */
- if (is_protocol || path_has_protocol(curr_bs->backing_file)) {
+ if (bdrv_backing_overridden(curr_bs)) {
+ /*
+ * If the backing file was overridden, we can only compare
+ * directly against the backing node's filename.
+ */
+
+ if (!filenames_refreshed) {
+ /*
+ * This will automatically refresh all of the
+ * filenames in the rest of the backing chain, so we
+ * only need to do this once.
+ */
+ bdrv_refresh_filename(bs_below);
+ filenames_refreshed = true;
+ }
+
+ if (strcmp(backing_file, bs_below->filename) == 0) {
+ retval = bs_below;
+ break;
+ }
+ } else if (is_protocol || path_has_protocol(curr_bs->backing_file)) {
+ /*
+ * If either of the filename paths is actually a protocol, then
+ * compare unmodified paths; otherwise make paths relative.
+ */
char *backing_file_full_ret;
if (strcmp(backing_file, curr_bs->backing_file) == 0) {
@@ -6820,7 +6839,7 @@ static bool append_strong_runtime_options(QDict *d, BlockDriverState *bs)
/* Note: This function may return false positives; it may return true
* even if opening the backing file specified by bs's image header
* would result in exactly bs->backing. */
-static bool bdrv_backing_overridden(BlockDriverState *bs)
+bool bdrv_backing_overridden(BlockDriverState *bs)
{
if (bs->backing) {
return strcmp(bs->auto_backing_file,