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libmount: minimize utimensat() write test usage 

utimensat() is pretty expensive when mounting parallel filesystems from
the same source. It's possible to ignore all this if mtab is not
writable.

Note that this change is irrelevant for default util-linux builds
where all around mtab is already disabled since v2.30 (commit
89958178f6).

This change is relevant only for users who still use --enable-libmount-support-mtab.

Reported-by: Douglas Jacobsen <dmjacobsen@lbl.gov>
Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2017-11-16 12:16:09 +01:00
parent b0a89709bf
commit 42ee788268
2 changed files with 21 additions and 9 deletions
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28
libmount/src/context_mount.c
View File

@ -998,7 +998,13 @@ int mnt_context_do_mount(struct libmnt_context *cxt)
#ifdef USE_LIBMOUNT_SUPPORT_MTAB
if (mnt_context_get_status(cxt)
&& !mnt_context_is_fake(cxt)
&& !cxt->helper) {
&& !cxt->helper
&& mnt_context_mtab_writable(cxt)) {
int is_rdonly = -1;
DBG(CXT, ul_debugobj(cxt, "checking for RDONLY mismatch"));
/*
* Mounted by mount(2), do some post-mount checks
*
@ -1007,11 +1013,13 @@ int mnt_context_do_mount(struct libmnt_context *cxt)
* avoid 'ro' in mtab and 'rw' in /proc/mounts.
*/
if ((cxt->mountflags & MS_BIND)
&& (cxt->mountflags & MS_RDONLY)
&& !mnt_is_readonly(mnt_context_get_target(cxt)))
&& (cxt->mountflags & MS_RDONLY)) {
mnt_context_set_mflags(cxt,
cxt->mountflags & ~MS_RDONLY);
if (is_rdonly < 0)
is_rdonly = mnt_is_readonly(mnt_context_get_target(cxt));
if (!is_rdonly)
mnt_context_set_mflags(cxt, cxt->mountflags & ~MS_RDONLY);
}
/* Kernel can silently add MS_RDONLY flag when mounting file
@ -1019,11 +1027,13 @@ int mnt_context_do_mount(struct libmnt_context *cxt)
* 'ro' in /proc/mounts and 'rw' in mtab.
*/
if (!(cxt->mountflags & (MS_RDONLY | MS_MOVE))
&& !mnt_context_propagation_only(cxt)
&& mnt_is_readonly(mnt_context_get_target(cxt)))
&& !mnt_context_propagation_only(cxt)) {
mnt_context_set_mflags(cxt,
cxt->mountflags | MS_RDONLY);
if (is_rdonly < 0)
is_rdonly = mnt_is_readonly(mnt_context_get_target(cxt));
if (is_rdonly)
mnt_context_set_mflags(cxt, cxt->mountflags | MS_RDONLY);
}
}
#endif

2
libmount/src/utils.c
View File

@ -216,6 +216,8 @@ int mnt_is_readonly(const char *path)
{
struct timespec times[2];
DBG(UTILS, ul_debug(" doing utimensat() based write test"));
times[0].tv_nsec = UTIME_NOW; /* atime */
times[1].tv_nsec = UTIME_OMIT; /* mtime */