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vfs: depessimize getfsstat when only the count is requested

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This avoids relocking mountlist_mtx for each entry.
This commit is contained in:
Mateusz Guzik 2020-07-10 06:47:58 +00:00
parent 8c1f410c19
commit 6c69e69724
1 changed files with 80 additions and 39 deletions
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119
sys/kern/vfs_syscalls.c
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@ -441,7 +441,46 @@ kern_getfsstat(struct thread *td, struct statfs **buf, size_t bufsize,
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 @@ kern_getfsstat(struct thread *td, struct statfs **buf, size_t bufsize,
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);
}
}
sfsp++;
}
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++;
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);
}