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
89958178f6d6ebe0944d423feaea66be521fff43).

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>

diff --git a/libmount/src/context_mount.c b/libmount/src/context_mount.c
index 79322c061c3a2e2e8423a6abbe91fb247f61e4fb..139fb5a287fb257f83c5160984fa0e222ce7d649 100644 (file)
--- a/libmount/src/context_mount.c
+++ b/libmount/src/context_mount.c
@@ -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
 

diff --git a/libmount/src/utils.c b/libmount/src/utils.c
index 5db5494d3adb7af2a97b01a0dab7b6e6b73f9f8c..56cdc206dd135c168aed0e742d710d862d27916d 100644 (file)
--- a/libmount/src/utils.c
+++ b/libmount/src/utils.c
@@ -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 */