On 2014-11-07 at 15:48, Jun Li wrote:
When bs->filename and bs->backing_file are relative pathname and not under the
same directory, path_combine() can not give the correct path for
bs->backing_file. So add get_localfile_absolute_path to get absolute path for
local file.
Well, for me it is the correct path. I'm using
$ mkdir -p foo
$ qemu-img create -f qcow2 foo/backing.qcow2 64M
$ qemu-img create -f qcow2 -b backing.qcow2 foo/backed.qcow2
I guess this patch will break that?
I know this isn't ideal, but that's just how it works, so we would break
existing usage.
Furthermore, compiling with this patch fails for me because on my system
readlink() and realpath() have the attribute warn_unused_result. Also,
I'm not sure, but readlink() may only resolve one link (which may point
to another link in turn).
And finally, with this patch applied and the return value issue fixed:
$ mkdir -p foo
$ qemu-img create -f qcow2 foo/backing.qcow2 64M
$ qemu-img create -f qcow2 -b foo/backing.qcow2 foo/backed.qcow2 64M
$ cd foo
$ qemu-img info backed.qcow2
lstat: No such file or directory
Because the backing field in the qcow2 file points to
"foo/backing.qcow2" which does not exist.
If you are giving a relative filename to the "-b" option during qemu-img
create, this filename is not (contrary to intuition) relative to the
current working directory of qemu-img, but it is the value which is put
directly into the backing field of the file to be created; and that
value is relative to that file's directory.
See also
http://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg00632.html
and http://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg00633.html
Max
e.g:
$ pwd
/tmp
$ /opt/qemu-git-arm/bin/qemu-img create -f qcow2 ./test 5M
Formatting './test', fmt=qcow2 size=5242880 encryption=off cluster_size=65536
lazy_refcounts=off
$ /opt/qemu-git-arm/bin/qemu-img create -f qcow2 ./tmp/test1 -b ./test
Formatting './tmp/test1', fmt=qcow2 size=5242880 backing_file='./test'
encryption=off cluster_size=65536 lazy_refcounts=off
$ /opt/qemu-git-arm/bin/qemu-img create -f qcow2 ./tmp/test2 -b ./tmp/test1
qemu-img: ./tmp/test2: Could not open './tmp/test1': Could not open backing
file: Could not open './tmp/./test': No such file or directory: No such file
or directory
This patch also fixes the following bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1161582#c2
Signed-off-by: Jun Li <[email protected]>
---
block.c | 28 +++++++++++++++++++++++++++-
include/block/block.h | 2 ++
2 files changed, 29 insertions(+), 1 deletion(-)
diff --git a/block.c b/block.c
index dacd881..5e2f669 100644
--- a/block.c
+++ b/block.c
@@ -259,6 +259,32 @@ int path_is_absolute(const char *path)
#endif
}
+void get_localfile_absolute_path(char *dest, int dest_size,
+ const char *filename)
+{
+ struct stat sb;
+ char *linkname;
+
+ if (path_is_absolute(filename)) {
+ pstrcpy(dest, dest_size, filename);
+ } else {
+ if (lstat(filename, &sb) == -1) {
+ perror("lstat");
+ exit(EXIT_FAILURE);
+ }
+
+ /* Check linkname is a link or not */
+ if (S_ISLNK(sb.st_mode)) {
+ linkname = malloc(sb.st_size + 1);
+ readlink(filename, linkname, sb.st_size + 1);
+ linkname[sb.st_size] = '\0';
+ realpath(linkname, dest);
+ } else {
+ realpath(filename, dest);
+ }
+ }
+}
+
/* if filename is absolute, just copy it to dest. Otherwise, build a
path to it by considering it is relative to base_path. URL are
supported. */
@@ -308,7 +334,7 @@ void bdrv_get_full_backing_filename(BlockDriverState *bs,
char *dest, size_t sz)
if (bs->backing_file[0] == '\0' || path_has_protocol(bs->backing_file)) {
pstrcpy(dest, sz, bs->backing_file);
} else {
- path_combine(dest, sz, bs->filename, bs->backing_file);
+ get_localfile_absolute_path(dest, sz, bs->backing_file);
}
}
diff --git a/include/block/block.h b/include/block/block.h
index 13e4537..6ddb150 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -398,6 +398,8 @@ void bdrv_get_full_backing_filename(BlockDriverState *bs,
int bdrv_is_snapshot(BlockDriverState *bs);
int path_is_absolute(const char *path);
+void get_localfile_absolute_path(char *dest, int dest_size,
+ const char *filename);
void path_combine(char *dest, int dest_size,
const char *base_path,
const char *filename);
