Author: mjg
Date: Fri Jul 10 06:47:58 2020
New Revision: 363069
URL: https://svnweb.freebsd.org/changeset/base/363069
Log:
vfs: depessimize getfsstat when only the count is requested
This avoids relocking mountlist_mtx for each entry.
Modified:
head/sys/kern/vfs_syscalls.c
Modified: head/sys/kern/vfs_syscalls.c
==============================================================================
--- head/sys/kern/vfs_syscalls.c Fri Jul 10 06:46:42 2020
(r363068)
+++ head/sys/kern/vfs_syscalls.c Fri Jul 10 06:47:58 2020
(r363069)
@@ -441,7 +441,46 @@ restart:
tofree = sfsp = *buf = malloc(maxcount * sizeof(struct statfs),
M_STATFS, M_WAITOK);
}
+
count = 0;
+
+ /*
+ * If there is no target buffer they only want the count.
+ *
+ * This could be TAILQ_FOREACH but it is open-coded to match the
original
+ * code below.
+ */
+ if (sfsp == NULL) {
+ mtx_lock(&mountlist_mtx);
+ for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
+ if (prison_canseemount(td->td_ucred, mp) != 0) {
+ nmp = TAILQ_NEXT(mp, mnt_list);
+ continue;
+ }
+#ifdef MAC
+ if (mac_mount_check_stat(td->td_ucred, mp) != 0) {
+ nmp = TAILQ_NEXT(mp, mnt_list);
+ continue;
+ }
+#endif
+ count++;
+ nmp = TAILQ_NEXT(mp, mnt_list);
+ }
+ mtx_unlock(&mountlist_mtx);
+ *countp = count;
+ return (0);
+ }
+
+ /*
+ * They want the entire thing.
+ *
+ * Short-circuit the corner case of no room for anything, avoids
+ * relocking below.
+ */
+ if (maxcount < 1) {
+ goto out;
+ }
+
mtx_lock(&mountlist_mtx);
for (mp = TAILQ_FIRST(&mountlist); mp != NULL; mp = nmp) {
if (prison_canseemount(td->td_ucred, mp) != 0) {
@@ -473,53 +512,55 @@ restart:
continue;
}
}
- if (sfsp != NULL && count < maxcount) {
- sp = &mp->mnt_stat;
- /*
- * If MNT_NOWAIT is specified, do not refresh
- * the fsstat cache.
- */
- if (mode != MNT_NOWAIT) {
- error = VFS_STATFS(mp, sp);
- if (error != 0) {
- mtx_lock(&mountlist_mtx);
- nmp = TAILQ_NEXT(mp, mnt_list);
- vfs_unbusy(mp);
- continue;
- }
+ sp = &mp->mnt_stat;
+ /*
+ * If MNT_NOWAIT is specified, do not refresh
+ * the fsstat cache.
+ */
+ if (mode != MNT_NOWAIT) {
+ error = VFS_STATFS(mp, sp);
+ if (error != 0) {
+ mtx_lock(&mountlist_mtx);
+ nmp = TAILQ_NEXT(mp, mnt_list);
+ vfs_unbusy(mp);
+ continue;
}
- if (priv_check_cred_vfs_generation(td->td_ucred)) {
- sptmp = malloc(sizeof(struct statfs), M_STATFS,
- M_WAITOK);
- *sptmp = *sp;
- sptmp->f_fsid.val[0] = sptmp->f_fsid.val[1] = 0;
- prison_enforce_statfs(td->td_ucred, mp, sptmp);
- sp = sptmp;
- } else
- sptmp = NULL;
- if (bufseg == UIO_SYSSPACE) {
- bcopy(sp, sfsp, sizeof(*sp));
- free(sptmp, M_STATFS);
- } else /* if (bufseg == UIO_USERSPACE) */ {
- error = copyout(sp, sfsp, sizeof(*sp));
- free(sptmp, M_STATFS);
- if (error != 0) {
- vfs_unbusy(mp);
- return (error);
- }
+ }
+ if (priv_check_cred_vfs_generation(td->td_ucred)) {
+ sptmp = malloc(sizeof(struct statfs), M_STATFS,
+ M_WAITOK);
+ *sptmp = *sp;
+ sptmp->f_fsid.val[0] = sptmp->f_fsid.val[1] = 0;
+ prison_enforce_statfs(td->td_ucred, mp, sptmp);
+ sp = sptmp;
+ } else
+ sptmp = NULL;
+ if (bufseg == UIO_SYSSPACE) {
+ bcopy(sp, sfsp, sizeof(*sp));
+ free(sptmp, M_STATFS);
+ } else /* if (bufseg == UIO_USERSPACE) */ {
+ error = copyout(sp, sfsp, sizeof(*sp));
+ free(sptmp, M_STATFS);
+ if (error != 0) {
+ vfs_unbusy(mp);
+ return (error);
}
- sfsp++;
}
+ sfsp++;
count++;
+
+ if (count == maxcount) {
+ vfs_unbusy(mp);
+ break;
+ }
+
mtx_lock(&mountlist_mtx);
nmp = TAILQ_NEXT(mp, mnt_list);
vfs_unbusy(mp);
}
mtx_unlock(&mountlist_mtx);
- if (sfsp != NULL && count > maxcount)
- *countp = maxcount;
- else
- *countp = count;
+out:
+ *countp = count;
return (0);
}
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