On Thu, Oct 01, 2020 at 09:06:31AM +0800, Ian Kent wrote:
> Some of the xfsprogs utilities read the mount table via. getmntent(3).
>
> The mount table may contain (almost always these days since /etc/mtab is
> symlinked to /proc/self/mounts) autofs mount entries. During processing
> of the mount table entries statfs(2) can be called on mount point paths
> which will trigger an automount if those entries are direct or offset
> autofs mount triggers (indirect autofs mounts aren't affected).
>
> This can be a problem when there are a lot of autofs direct or offset
> mounts because real mounts will be triggered when statfs(2) is called.
> This can be particularly bad if the triggered mounts are NFS mounts and
> the server is unavailable leading to lengthy boot times or worse.
>
> Simply ignoring autofs mount entries during getmentent(3) traversals
> avoids the statfs() call that triggers these mounts. If there are
> automounted mounts (real mounts) at the time of reading the mount table
> these will still be seen in the list so they will be included if that
> actually matters to the reader.
>
> Recent glibc getmntent(3) can ignore autofs mounts but that requires the
> autofs user to configure autofs to use the "ignore" pseudo mount option
> for autofs mounts. But this isn't yet the autofs default (to prevent
> unexpected side effects) so that can't be used.
>
> The autofs direct and offset automount triggers are pseudo file system
> mounts and are more or less useless in terms on file system information
> so excluding them doesn't sacrifice useful file system information
> either.
>
> Consequently excluding autofs mounts shouldn't have any adverse side
> effects.
>
> Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
> ---
> fsr/xfs_fsr.c | 3 +++
> libfrog/linux.c | 2 ++
> libfrog/paths.c | 2 ++
> 3 files changed, 7 insertions(+)
>
> diff --git a/fsr/xfs_fsr.c b/fsr/xfs_fsr.c
> index 77a10a1d..466ad9e4 100644
> --- a/fsr/xfs_fsr.c
> +++ b/fsr/xfs_fsr.c
> @@ -323,6 +323,9 @@ initallfs(char *mtab)
> while ((mnt = platform_mntent_next(&cursor)) != NULL) {
> int rw = 0;
>
> + if (!strcmp(mnt->mnt_type, "autofs"))
> + continue;
Hmm... the libfrog changes look decent, but it strikes me as a little
odd that we don't just make platform_mntent_next filter that out?
(Or I guess refactor fsr to use the fs table...)
OTOH "Not _another_ herring^Wrefactor!"
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> +
> if (strcmp(mnt->mnt_type, MNTTYPE_XFS ) != 0 ||
> stat(mnt->mnt_fsname, &sb) == -1 ||
> !S_ISBLK(sb.st_mode))
> diff --git a/libfrog/linux.c b/libfrog/linux.c
> index 40a839d1..a45d99ab 100644
> --- a/libfrog/linux.c
> +++ b/libfrog/linux.c
> @@ -73,6 +73,8 @@ platform_check_mount(char *name, char *block, struct stat *s, int flags)
> * servers. So first, a simple check: does the "dev" start with "/" ?
> */
> while ((mnt = getmntent(f)) != NULL) {
> + if (!strcmp(mnt->mnt_type, "autofs"))
> + continue;
> if (mnt->mnt_fsname[0] != '/')
> continue;
> if (stat(mnt->mnt_dir, &mst) < 0)
> diff --git a/libfrog/paths.c b/libfrog/paths.c
> index 32737223..d6793764 100644
> --- a/libfrog/paths.c
> +++ b/libfrog/paths.c
> @@ -389,6 +389,8 @@ fs_table_initialise_mounts(
> return errno;
>
> while ((mnt = getmntent(mtp)) != NULL) {
> + if (!strcmp(mnt->mnt_type, "autofs"))
> + ^continue;
> if (!realpath(mnt->mnt_dir, rmnt_dir))
> continue;
> if (!realpath(mnt->mnt_fsname, rmnt_fsname))
>
>
