Image below user cases: case 1: ``` $ qemu-img create -f raw source.raw 1G $ qemu-img create -f qcow2 -F raw -b source.raw ./source.raw qemu-img info source.raw image: source.raw file format: qcow2 virtual size: 193K (197120 bytes) disk size: 196K cluster_size: 65536 backing file: source.raw <<<<<< backing file format: raw Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false ```
case 2: ``` $ qemu-img create -f raw source.raw 1G $ ln -sf source.raw destination.qcow2 $ qemu-img create -f qcow2 -F raw -b source.raw ./destination.qcow2 qemu-img info source.raw image: source.raw file format: qcow2 <<<<<< virtual size: 2.0G (2147483648 bytes) disk size: 196K cluster_size: 65536 backing file: source.raw backing file format: raw Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false ``` Generally, we don't expect to corrupte the source.raw anyway, while actually it does. Here we check their inode number instead of file name. Suggested-by: Daniel P. Berrangé <berra...@redhat.com> Signed-off-by: Li Zhijian <lizhij...@cn.fujitsu.com> --- v2: utilize stat() instead of realpath() (Daniel) Signed-off-by: Li Zhijian <lizhij...@cn.fujitsu.com> --- block.c | 39 ++++++++++++++++++++++++++++++++------- 1 file changed, 32 insertions(+), 7 deletions(-) diff --git a/block.c b/block.c index 9ad725d205..db4ae57959 100644 --- a/block.c +++ b/block.c @@ -6431,6 +6431,37 @@ bool bdrv_op_blocker_is_empty(BlockDriverState *bs) return true; } +static bool validate_backing_file(const char *filename, + const char *backing_file, Error **errp) +{ + struct stat filename_stat, backing_stat; + + if (backing_file[0] == '\0') { + error_setg(errp, "Expected backing file name, got empty string"); + goto out; + } + + /* check whether filename and backing_file are refering to the same file */ + if (stat(backing_file, &backing_stat) == -1) { + error_setg(errp, "Cannot stat backing file %s", backing_file); + goto out; + } + if (stat(filename, &filename_stat) == -1) { + /* Simply consider filename doesn't exist, no need to further check */ + return true; + } + if ((filename_stat.st_dev == backing_stat.st_dev) && + (filename_stat.st_ino == backing_stat.st_ino)) { + error_setg(errp, "Error: Trying to create an image with the " + "same filename as the backing file"); + goto out; + } + + return true; +out: + return false; +} + void bdrv_img_create(const char *filename, const char *fmt, const char *base_filename, const char *base_fmt, char *options, uint64_t img_size, int flags, bool quiet, @@ -6507,13 +6538,7 @@ void bdrv_img_create(const char *filename, const char *fmt, backing_file = qemu_opt_get(opts, BLOCK_OPT_BACKING_FILE); if (backing_file) { - if (!strcmp(filename, backing_file)) { - error_setg(errp, "Error: Trying to create an image with the " - "same filename as the backing file"); - goto out; - } - if (backing_file[0] == '\0') { - error_setg(errp, "Expected backing file name, got empty string"); + if (!validate_backing_file(filename, backing_file, errp)) { goto out; } } -- 2.30.2