coda: stop using 'struct timespec' in user API

We exchange file timestamps with user space using psdev device
read/write operations with a fixed but architecture specific binary
layout.

On 32-bit systems, this uses a 'timespec' structure that is defined by
the C library to contain two 32-bit values for seconds and nanoseconds.
As we get ready for the year 2038 overflow of the 32-bit signed seconds,
the kernel now uses 64-bit timestamps internally, and user space will do
the same change by changing the 'timespec' definition in the future.

Unfortunately, this breaks the layout of the coda_vattr structure, so we
need to redefine that in terms of something that does not change.  I'm
introducing a new 'struct vtimespec' structure here that keeps the
existing layout, and the same change has to be done in the coda user
space copy of linux/coda.h before anyone can use that on a 32-bit
architecture with 64-bit time_t.

An open question is what should happen to actual times past y2038, as
they are now truncated to the last valid date when sent to user space,
and interpreted as pre-1970 times when a timestamp with the MSB set is
read back into the kernel.  Alternatively, we could change the new
timespec64_to_coda()/coda_to_timespec64() functions to use a different
interpretation and extend the available range further to the future by
disallowing past timestamps.  This would require more changes in the
user space side though.

Link: http://lkml.kernel.org/r/562b7324149461743e4fbe2fedbf7c242f7e274a.1558117389.git.jaharkes@cs.cmu.edu
Link: https://patchwork.kernel.org/patch/10474735/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Acked-by: Jan Harkes <jaharkes@cs.cmu.edu>
Cc: Colin Ian King <colin.king@canonical.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Mikko Rapeli <mikko.rapeli@iki.fi>
Cc: Sam Protsenko <semen.protsenko@linaro.org>
Cc: Yann Droneaud <ydroneaud@opteya.com>
Cc: Zhouyang Jia <jiazhouyang09@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 3 deletions

diff --git a/include/uapi/linux/coda.h b/include/uapi/linux/coda.h
index ed8cb263e482..fc5f7874208a 100644
--- a/include/uapi/linux/coda.h
+++ b/include/uapi/linux/coda.h
@@ -211,6 +211,20 @@ struct CodaFid {
  */
 enum coda_vtype	{ C_VNON, C_VREG, C_VDIR, C_VBLK, C_VCHR, C_VLNK, C_VSOCK, C_VFIFO, C_VBAD };
 
+#ifdef __linux__
+/*
+ * This matches the traditional Linux 'timespec' structure binary layout,
+ * before using 64-bit time_t everywhere. Overflows in y2038 on 32-bit
+ * architectures.
+ */
+struct vtimespec {
+	long		tv_sec;		/* seconds */
+	long		tv_nsec;	/* nanoseconds */
+};
+#else
+#define vtimespec timespec
+#endif
+
 struct coda_vattr {
 	long     	va_type;	/* vnode type (for create) */
 	u_short		va_mode;	/* files access mode and type */
@@ -220,9 +234,9 @@ struct coda_vattr {
 	long		va_fileid;	/* file id */
 	u_quad_t	va_size;	/* file size in bytes */
 	long		va_blocksize;	/* blocksize preferred for i/o */
-	struct timespec	va_atime;	/* time of last access */
-	struct timespec	va_mtime;	/* time of last modification */
-	struct timespec	va_ctime;	/* time file changed */
+	struct vtimespec va_atime;	/* time of last access */
+	struct vtimespec va_mtime;	/* time of last modification */
+	struct vtimespec va_ctime;	/* time file changed */
 	u_long		va_gen;		/* generation number of file */
 	u_long		va_flags;	/* flags defined for file */
 	cdev_t	        va_rdev;	/* device special file represents */