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[PULL,21/79] util: use fcntl() for qemu_write_pidfile() locking

Message ID 1538295197-23704-22-git-send-email-pbonzini@redhat.com
State New
Headers show
Series [PULL,01/79] virtio: Return true from virtio_queue_empty if broken | expand

Commit Message

Paolo Bonzini Sept. 30, 2018, 8:12 a.m. UTC 
From: Marc-André Lureau <marcandre.lureau@redhat.com>

Daniel Berrangé suggested to use fcntl() locks rather than lockf().

'man lockf':

   On Linux, lockf() is just an interface on top of fcntl(2) locking.
   Many other systems implement lockf() in this way, but note that
   POSIX.1 leaves the relationship between lockf() and fcntl(2) locks
   unspecified.  A portable application should probably avoid mixing
   calls to these interfaces.

IOW, if its just a shim around fcntl() on many systems, it is clearer
if we just use fcntl() directly, as we then know how fcntl() locks will
behave if they're on a network filesystem like NFS.

Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180831145314.14736-3-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 util/oslib-posix.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index 0e3ab9d..fbd0dc8 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -95,6 +95,11 @@  bool qemu_write_pidfile(const char *path, Error **errp)
 
     while (1) {
         struct stat a, b;
+        struct flock lock = {
+            .l_type = F_WRLCK,
+            .l_whence = SEEK_SET,
+            .l_len = 0,
+        };
 
         fd = qemu_open(path, O_CREAT | O_WRONLY, S_IRUSR | S_IWUSR);
         if (fd == -1) {
@@ -107,7 +112,7 @@  bool qemu_write_pidfile(const char *path, Error **errp)
             goto fail_close;
         }
 
-        if (lockf(fd, F_TLOCK, 0) < 0) {
+        if (fcntl(fd, F_SETLK, &lock)) {
             error_setg_errno(errp, errno, "Cannot lock pid file");
             goto fail_close;
         }