[dm-devel] [PATCH] kpartx: Improve finding loopback device by file
Martin Wilck
mwilck at suse.com
Mon Feb 5 10:32:13 UTC 2018
On Mon, 2018-02-05 at 09:58 +0100, Julian Andres Klode wrote:
> Commit 9bdfa3eb8e24b668e6c2bb882cddb0ccfe23ed5b changed kpartx
> to lookup files by absolute path, using realpath(). This introduced
> a regression when part of the filename where symbolic links. While
> the kernel stores the absolute path to the backing file, it does not
> resolve symbolic links, and hence kpartx would fail to find the
> loopback
> device because it resolves symbolic links when deleting.
>
> This introduces two workarounds in find_loop_by_file()
>
> (1) We match against the specified file name as is as well
> (2) We canonicalize the loopinfo.lo_name and match the canonicalized
> filename
> against that.
>
> Bug-Ubuntu: https://bugs.launchpad.net/ubuntu/+source/multipath-tools
> /+bug/1747044
> Signed-off-by: Julian Andres Klode <julian.klode at canonical.com>
> ---
> kpartx/kpartx.c | 8 +-------
> kpartx/lopart.c | 12 +++++++++++-
> 2 files changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/kpartx/kpartx.c b/kpartx/kpartx.c
> index 442b6bd9..c1af1c5e 100644
> --- a/kpartx/kpartx.c
> +++ b/kpartx/kpartx.c
> @@ -327,13 +327,7 @@ main(int argc, char **argv){
>
> if (S_ISREG (buf.st_mode)) {
> /* already looped file ? */
> - char rpath[PATH_MAX];
> - if (realpath(device, rpath) == NULL) {
> - fprintf(stderr, "Error: %s: %s\n", device,
> - strerror(errno));
> - exit (1);
> - }
> - loopdev = find_loop_by_file(rpath);
> + loopdev = find_loop_by_file(device);
>
> if (!loopdev && what == DELETE)
> exit (0);
> diff --git a/kpartx/lopart.c b/kpartx/lopart.c
> index 02b29e8c..26b2678c 100644
> --- a/kpartx/lopart.c
> +++ b/kpartx/lopart.c
> @@ -69,6 +69,13 @@ char *find_loop_by_file(const char *filename)
> struct loop_info loopinfo;
> const char VIRT_BLOCK[] = "/sys/devices/virtual/block";
> char path[PATH_MAX];
> + char rfilename[PATH_MAX];
> + char rloopfilename[PATH_MAX];
> + if (realpath(filename, rfilename) == NULL) {
> + fprintf(stderr, "Error: %s: %s\n", filename,
> + strerror(errno));
> + exit (1);
> + }
>
> dir = opendir(VIRT_BLOCK);
> if (!dir)
> @@ -117,7 +124,10 @@ char *find_loop_by_file(const char *filename)
>
> close (fd);
>
> - if (0 == strcmp(filename, loopinfo.lo_name)) {
> + if (0 == strcmp(filename, loopinfo.lo_name) ||
> + 0 == strcmp(rfilename, loopinfo.lo_name) ||
> + (realpath(loopinfo.lo_name, rloopfilename) &&
> + 0 == strcmp(rfilename, rloopfilename))) {
> found = realpath(path, NULL);
> break;
> }
That "if x matches y or x matches y' or x' matches y" feels like
guesswork. Can't we simply call realpath() on both loopinfo.lo_name and
filename, and compare the two?
Martin
--
Dr. Martin Wilck <mwilck at suse.com>, Tel. +49 (0)911 74053 2107
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
More information about the dm-devel
mailing list