svn commit: r356830 - in head: lib/libc/gen lib/libc/sys sys/fs/unionfs sys/kern sys/sys
Mateusz Guzik
mjg at FreeBSD.org
Fri Jan 17 14:42:27 UTC 2020
Author: mjg
Date: Fri Jan 17 14:42:25 2020
New Revision: 356830
URL: https://svnweb.freebsd.org/changeset/base/356830
Log:
vfs: provide F_ISUNIONSTACK as a kludge for libc
Prior to introduction of this op libc's readdir would call fstatfs(2), in
effect unnecessarily copying kilobytes of data just to check fs name and a
mount flag.
Reviewed by: kib (previous version)
Differential Revision: https://reviews.freebsd.org/D23162
Modified:
head/lib/libc/gen/opendir.c
head/lib/libc/sys/fcntl.2
head/sys/fs/unionfs/union_vfsops.c
head/sys/kern/kern_descrip.c
head/sys/sys/fcntl.h
head/sys/sys/mount.h
Modified: head/lib/libc/gen/opendir.c
==============================================================================
--- head/lib/libc/gen/opendir.c Fri Jan 17 14:40:09 2020 (r356829)
+++ head/lib/libc/gen/opendir.c Fri Jan 17 14:42:25 2020 (r356830)
@@ -273,7 +273,25 @@ _filldir(DIR *dirp, bool use_current_pos)
return (true);
}
+static bool
+is_unionstack(int fd)
+{
+ struct statfs sfb;
+ int unionstack;
+ unionstack = _fcntl(fd, F_ISUNIONSTACK);
+ if (unionstack != -1)
+ return (unionstack);
+
+ /*
+ * Temporary compat for kernels which don't provide F_ISUNIONSTACK.
+ */
+ if (_fstatfs(fd, &sfb) < 0)
+ return (true);
+ return (strcmp(sfb.f_fstypename, "unionfs") == 0 ||
+ (sfb.f_flags & MNT_UNION));
+}
+
/*
* Common routine for opendir(3), __opendir2(3) and fdopendir(3).
*/
@@ -312,12 +330,7 @@ __opendir_common(int fd, int flags, bool use_current_p
*/
unionstack = false;
if (flags & DTF_NODUP) {
- struct statfs sfb;
-
- if (_fstatfs(fd, &sfb) == 0) {
- unionstack = strcmp(sfb.f_fstypename, "unionfs") == 0 ||
- (sfb.f_flags & MNT_UNION);
- }
+ unionstack = is_unionstack(fd);
}
if (unionstack) {
Modified: head/lib/libc/sys/fcntl.2
==============================================================================
--- head/lib/libc/sys/fcntl.2 Fri Jan 17 14:40:09 2020 (r356829)
+++ head/lib/libc/sys/fcntl.2 Fri Jan 17 14:42:25 2020 (r356830)
@@ -28,7 +28,7 @@
.\" @(#)fcntl.2 8.2 (Berkeley) 1/12/94
.\" $FreeBSD$
.\"
-.Dd September 4, 2019
+.Dd January 17, 2020
.Dt FCNTL 2
.Os
.Sh NAME
@@ -185,6 +185,11 @@ Add seals to the file as described below, if the under
seals.
.It Dv F_GET_SEALS
Get seals associated with the file, if the underlying filesystem supports seals.
+.It Dv F_ISUNIONSTACK
+Check if the vnode is part of a union stack (either the "union" flag from
+.Xr mount 2
+or unionfs).
+This is a hack not intended to be used outside of libc.
.El
.Pp
The flags for the
Modified: head/sys/fs/unionfs/union_vfsops.c
==============================================================================
--- head/sys/fs/unionfs/union_vfsops.c Fri Jan 17 14:40:09 2020 (r356829)
+++ head/sys/fs/unionfs/union_vfsops.c Fri Jan 17 14:42:25 2020 (r356830)
@@ -296,7 +296,7 @@ unionfs_domount(struct mount *mp)
if ((ump->um_lowervp->v_mount->mnt_flag & MNT_LOCAL) &&
(ump->um_uppervp->v_mount->mnt_flag & MNT_LOCAL))
mp->mnt_flag |= MNT_LOCAL;
- mp->mnt_kern_flag |= MNTK_NOMSYNC;
+ mp->mnt_kern_flag |= MNTK_NOMSYNC | MNTK_UNIONFS;
MNT_IUNLOCK(mp);
/*
Modified: head/sys/kern/kern_descrip.c
==============================================================================
--- head/sys/kern/kern_descrip.c Fri Jan 17 14:40:09 2020 (r356829)
+++ head/sys/kern/kern_descrip.c Fri Jan 17 14:42:25 2020 (r356830)
@@ -489,6 +489,7 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_
struct filedescent *fde;
struct proc *p;
struct vnode *vp;
+ struct mount *mp;
int error, flg, seals, tmp;
uint64_t bsize;
off_t foffset;
@@ -813,6 +814,49 @@ kern_fcntl(struct thread *td, int fd, int cmd, intptr_
atomic_clear_int(&fp->f_flag, FRDAHEAD);
}
VOP_UNLOCK(vp);
+ fdrop(fp, td);
+ break;
+
+ case F_ISUNIONSTACK:
+ /*
+ * Check if the vnode is part of a union stack (either the
+ * "union" flag from mount(2) or unionfs).
+ *
+ * Prior to introduction of this op libc's readdir would call
+ * fstatfs(2), in effect unnecessarily copying kilobytes of
+ * data just to check fs name and a mount flag.
+ *
+ * Fixing the code to handle everything in the kernel instead
+ * is a non-trivial endeavor and has low priority, thus this
+ * horrible kludge facilitates the current behavior in a much
+ * cheaper manner until someone(tm) sorts this out.
+ */
+ error = fget_unlocked(fdp, fd, &cap_no_rights, &fp, NULL);
+ if (error != 0)
+ break;
+ if (fp->f_type != DTYPE_VNODE) {
+ fdrop(fp, td);
+ error = EBADF;
+ break;
+ }
+ vp = fp->f_vnode;
+ /*
+ * Since we don't prevent dooming the vnode even non-null mp
+ * found can become immediately stale. This is tolerable since
+ * mount points are type-stable (providing safe memory access)
+ * and any vfs op on this vnode going forward will return an
+ * error (meaning return value in this case is meaningless).
+ */
+ mp = (struct mount *)atomic_load_ptr(&vp->v_mount);
+ if (__predict_false(mp == NULL)) {
+ fdrop(fp, td);
+ error = EBADF;
+ break;
+ }
+ td->td_retval[0] = 0;
+ if (mp->mnt_kern_flag & MNTK_UNIONFS ||
+ mp->mnt_flag & MNT_UNION)
+ td->td_retval[0] = 1;
fdrop(fp, td);
break;
Modified: head/sys/sys/fcntl.h
==============================================================================
--- head/sys/sys/fcntl.h Fri Jan 17 14:40:09 2020 (r356829)
+++ head/sys/sys/fcntl.h Fri Jan 17 14:42:25 2020 (r356830)
@@ -250,6 +250,7 @@ typedef __pid_t pid_t;
#define F_DUP2FD_CLOEXEC 18 /* Like F_DUP2FD, but FD_CLOEXEC is set */
#define F_ADD_SEALS 19
#define F_GET_SEALS 20
+#define F_ISUNIONSTACK 21 /* Kludge for libc, don't use it. */
/* Seals (F_ADD_SEALS, F_GET_SEALS). */
#define F_SEAL_SEAL 0x0001 /* Prevent adding sealings */
Modified: head/sys/sys/mount.h
==============================================================================
--- head/sys/sys/mount.h Fri Jan 17 14:40:09 2020 (r356829)
+++ head/sys/sys/mount.h Fri Jan 17 14:42:25 2020 (r356830)
@@ -414,6 +414,7 @@ void __mnt_vnode_markerfree_lazy(struct vnode
#define MNTK_USES_BCACHE 0x00004000 /* FS uses the buffer cache. */
#define MNTK_TEXT_REFS 0x00008000 /* Keep use ref for text */
#define MNTK_VMSETSIZE_BUG 0x00010000
+#define MNTK_UNIONFS 0x00020000 /* A hack for F_ISUNIONSTACK */
#define MNTK_NOASYNC 0x00800000 /* disable async */
#define MNTK_UNMOUNT 0x01000000 /* unmount in progress */
#define MNTK_MWAIT 0x02000000 /* waiting for unmount to finish */
More information about the svn-src-all
mailing list