[PATCH] flock: make flock(3) work on NFSv4

[Petr Uzel <petr.uzel@suse.cz>]

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To pleace an exclusive lock on a file, NFSv4 requires
the file to be opened RW because of the emulation of flock()
by fcntl():

http://www.spinics.net/lists/linux-nfs/msg18502.html

So instead of O_RDONLY, open the file in O_RDWR if access()
indicates it is possible (unless shared lock is requested).

From: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Petr Uzel <petr.uzel@suse.cz>
---
 sys-utils/flock.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/sys-utils/flock.c b/sys-utils/flock.c
index 7d321de..a500319 100644
--- a/sys-utils/flock.c
+++ b/sys-utils/flock.c
@@ -129,6 +129,7 @@ int main(int argc, char *argv[])
   int have_timeout = 0;
   int type = LOCK_EX;
   int block = 0;
+  int open_accmode;
   int fd = -1;
   int opt, ix;
   int do_close = 0;
@@ -211,9 +212,11 @@ int main(int argc, char *argv[])
     }
 
     filename = argv[optind];
-    fd = open(filename, O_RDONLY|O_NOCTTY|O_CREAT, 0666);
+    open_accmode = ((type == LOCK_SH || access(filename, R_OK|W_OK) < 0) ?
+                    O_RDONLY : O_RDWR);
+    fd = open(filename, open_accmode|O_NOCTTY|O_CREAT, 0666);
     /* Linux doesn't like O_CREAT on a directory, even though it should be a
-       no-op */
+       no-op; POSIX doesn't allow O_RDWR or O_WRONLY */
     if (fd < 0 && errno == EISDIR)
         fd = open(filename, O_RDONLY|O_NOCTTY);
 
-- 
1.7.3.4


Petr

--
Petr Uzel
IRC: ptr_uzl @ freenode

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