On Thu, 2020-10-08 at 15:03 -0500, Eric Sandeen wrote:
> On 10/7/20 8:52 PM, 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.
>
> (usually this'd go below the "---")
>
> > Changes since v1:
> > - drop hunk from fsr/xfs_fsr.c.
> >
> > Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
> > ---
> > libfrog/linux.c | 2 ++
> > libfrog/paths.c | 2 ++
> > 2 files changed, 4 insertions(+)
> >
> > 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;
>
> I may change the order of this test and the next, just so it
> continues to
> align with the comment above. Shouldn't make any difference, right?
Yep, no difference to resolving the problem.
The only reason for it to be first is cases where there's say, 40 or
50 mounts and a thousand or more autofs direct mounts. Then every
test you do before skipping the autofs entry adds a thousand or more
tests to the traversal.
Ian
>
> Otherwise:
>
> Reviewed-by: Eric Sandeen <sandeen@xxxxxxxxxx>
>
> > 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))
> >
> >
