On 27.07.20 14:27, Andrey Shinkevich wrote: > On 25.06.2020 18:22, Max Reitz wrote: >> 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. In order not to >> change our externally visible behavior (incompatibly), we have to let >> bdrv_query_image_info() try to get the image format from bs->backing if >> bs->backing_format is unset. (The QAPI schema describes >> backing-filename-format as "the format of the backing file", so it is >> not necessarily what the image header says, but just the format of the >> file referenced by backing-filename (if known).) >> >> 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. >> >> Signed-off-by: Max Reitz <[email protected]> >> --- >> include/block/block_int.h | 21 ++++++++++++++++----- >> block.c | 35 +++++++++++++++++++++++++++-------- >> block/qapi.c | 17 +++++++++++++---- >> tests/qemu-iotests/228 | 6 +++--- >> tests/qemu-iotests/228.out | 6 +++--- >> tests/qemu-iotests/245 | 4 +++- >> 6 files changed, 65 insertions(+), 24 deletions(-) >> > ... >> diff --git a/block/qapi.c b/block/qapi.c >> index 2628323b63..5da6d7e6e0 100644 >> --- a/block/qapi.c >> +++ b/block/qapi.c >> @@ -47,7 +47,7 @@ BlockDeviceInfo *bdrv_block_device_info(BlockBackend >> *blk, >> Error **errp) >> { >> ImageInfo **p_image_info; >> - BlockDriverState *bs0; >> + BlockDriverState *bs0, *backing; >> BlockDeviceInfo *info; >> if (!bs->drv) { >> @@ -76,9 +76,10 @@ BlockDeviceInfo >> *bdrv_block_device_info(BlockBackend *blk, >> info->node_name = g_strdup(bs->node_name); >> } >> - if (bs->backing_file[0]) { >> + backing = bdrv_cow_bs(bs); >> + if (backing) { >> info->has_backing_file = true; >> - info->backing_file = g_strdup(bs->backing_file); >> + info->backing_file = g_strdup(backing->filename); >> } >> if (!QLIST_EMPTY(&bs->dirty_bitmaps)) { >> @@ -314,6 +315,8 @@ void bdrv_query_image_info(BlockDriverState *bs, >> backing_filename = bs->backing_file; >> if (backing_filename[0] != '\0') { >> char *backing_filename2; >> + const char *backing_format = NULL; >> + >> info->backing_filename = g_strdup(backing_filename); >> info->has_backing_filename = true; >> backing_filename2 = bdrv_get_full_backing_filename(bs, NULL); >> @@ -326,7 +329,13 @@ void bdrv_query_image_info(BlockDriverState *bs, >> } >> if (bs->backing_format[0]) { >> - info->backing_filename_format = >> g_strdup(bs->backing_format); >> + backing_format = bs->backing_format; >> + } else if (bs->backing && bs->backing->bs->drv && >> + !bdrv_backing_overridden(bs)) { >> + backing_format = bs->backing->bs->drv->format_name; >> + } > > > In case bdrv_backing_overridden() returns true , should we invoke > bdrv_refresh_filename() and assign the format_name then?
I don’t think so. The format we return in info->backing_filename_format should be the format of the file returned in info->backing_filename. The latter is bs->backing_file, which (as of this patch), is the backing file as reported by the image header. Therefore, if the backing file was overridden, we cannot assume that bs->backing->bs refers to the same file as bs->backing_file, and so we cannot assume bs->backing->bs->drv->format_name to be info->backing_filename’s format. Max
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