From 35f7f3fb5c65dcdf8315bbfd40a3c1d015663d77 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= Date: Fri, 31 Aug 2018 16:53:13 +0200 Subject: [PATCH] util: use fcntl() for qemu_write_pidfile() locking MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Marc-André Lureau Message-Id: <20180831145314.14736-3-marcandre.lureau@redhat.com> Signed-off-by: Paolo Bonzini --- util/oslib-posix.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/util/oslib-posix.c b/util/oslib-posix.c index 0e3ab9d959..fbd0dc8c57 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; }