Extend the KPI to lock and unlock f_offset member of struct file. It

now fully encapsulates all accesses to f_offset, and extends f_offset
locking to other consumers that need it, in particular, to lseek() and
variants of getdirentries().

Ensure that on 32bit architectures f_offset, which is 64bit quantity,
always read and written under the mtxpool protection. This fixes
apparently easy to trigger race when parallel lseek()s or lseek() and
read/write could destroy file offset.

The already broken ABI emulations, including iBCS and SysV, are not
converted (yet).

Tested by:	pho
No objections from:	jhb
MFC after:    3 weeks

1 files changed, 16 insertions, 1 deletions

diff --git a/sys/sys/file.h b/sys/sys/file.h
index b89e584..c4c6dbf 100644
--- a/sys/sys/file.h
+++ b/sys/sys/file.h
@@ -72,10 +72,25 @@ struct socket;
 struct file;
 struct ucred;
 
+#define	FOF_OFFSET	0x01	/* Use the offset in uio argument */
+#define	FOF_NOLOCK	0x02	/* Do not take FOFFSET_LOCK */
+#define	FOF_NEXTOFF	0x04	/* Also update f_nextoff */
+#define	FOF_NOUPDATE	0x10	/* Do not update f_offset */
+off_t foffset_lock(struct file *fp, int flags);
+void foffset_lock_uio(struct file *fp, struct uio *uio, int flags);
+void foffset_unlock(struct file *fp, off_t val, int flags);
+void foffset_unlock_uio(struct file *fp, struct uio *uio, int flags);
+
+static inline off_t
+foffset_get(struct file *fp)
+{
+
+	return (foffset_lock(fp, FOF_NOLOCK));
+}
+
 typedef int fo_rdwr_t(struct file *fp, struct uio *uio,
 		    struct ucred *active_cred, int flags,
 		    struct thread *td);
-#define	FOF_OFFSET	1	/* Use the offset in uio argument */
 typedef	int fo_truncate_t(struct file *fp, off_t length,
 		    struct ucred *active_cred, struct thread *td);
 typedef	int fo_ioctl_t(struct file *fp, u_long com, void *data,