The Linux kernel expects a flock64 structure whenever you use OFD locks
with fcntl64. Unfortunately, you can currently build a 32-bit program
that passes in a struct flock when it calls fcntl64.
Only define the F_OFD_* constants when __USE_FILE_OFFSET64 is also
defined, so that the build fails in this situation rather than
producing a broken binary.
Reported-by: Cyril Hrubis <chrubis@xxxxxxx>
Cc: Michael Kerrisk (man-pages) <mtk.manpages@xxxxxxxxx>
Cc: Carlos O'Donell <carlos@xxxxxxxxxx>
Cc: Yuriy Kolerov <Yuriy.Kolerov@xxxxxxxxxxxx>
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
manual/examples/ofdlocks.c | 1 +
manual/llio.texi | 8 +++++---
sysdeps/unix/sysv/linux/bits/fcntl-linux.h | 15 +++++++++++----
3 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/manual/examples/ofdlocks.c b/manual/examples/ofdlocks.c
index ba4f0ef4d237..6df18ce5c368 100644
--- a/manual/examples/ofdlocks.c
+++ b/manual/examples/ofdlocks.c
@@ -15,6 +15,7 @@
along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
+/* Note that this must be built with -D_FILE_OFFSET_BITS=64 on 32-bit arch */
#define _GNU_SOURCE
#include <stdio.h>
#include <sys/types.h>
diff --git a/manual/llio.texi b/manual/llio.texi
index 019dea2c3189..99c700833641 100644
--- a/manual/llio.texi
+++ b/manual/llio.texi
@@ -3907,9 +3907,11 @@ descriptor.
Open file description locks use the same @code{struct flock} as
process-associated locks as an argument (@pxref{File Locks}) and the
-macros for the @code{command} values are also declared in the header file
-@file{fcntl.h}. To use them, the macro @code{_GNU_SOURCE} must be
-defined prior to including any header file.
+macros for the @code{command} values are also declared in the header
+file @file{fcntl.h}. To use them, the macro @code{_GNU_SOURCE} must be
+defined prior to including any header file. Additionally, if building on
+a 32-bit architecture, then large file offsets must also be enabled
+by defining @code{_FILE_OFFSET_BITS == 64}.
In contrast to process-associated locks, any @code{struct flock} used as
an argument to open file description lock commands must have the @code{l_pid}
diff --git a/sysdeps/unix/sysv/linux/bits/fcntl-linux.h b/sysdeps/unix/sysv/linux/bits/fcntl-linux.h
index 7e5b0aecdcb4..7f3c9fef627f 100644
--- a/sysdeps/unix/sysv/linux/bits/fcntl-linux.h
+++ b/sysdeps/unix/sysv/linux/bits/fcntl-linux.h
@@ -127,11 +127,18 @@
This means that they are inherited across fork or clone with CLONE_FILES
like BSD (flock) locks, and they are only released automatically when the
last reference to the the file description against which they were acquired
- is put. */
+ is put.
+
+ Note that the kernel does not support the legacy struct flock on 32-bit
+ arches with OFD locks. On those arches you need define both _GNU_SOURCE
+ and _FILE_OFFSET_BITS=64.
+ */
#ifdef __USE_GNU
-# define F_OFD_GETLK 36
-# define F_OFD_SETLK 37
-# define F_OFD_SETLKW 38
+# if __WORDSIZE != 32 || defined __USE_FILE_OFFSET64
+# define F_OFD_GETLK 36
+# define F_OFD_SETLK 37
+# define F_OFD_SETLKW 38
+# endif
#endif
#ifdef __USE_LARGEFILE64
--
2.7.4
--
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