[Qemu-devel] [PATCH v5 08/27] osdep: Add qemu_lock_fd and qemu_unlock_fd

[Fam Zheng <famz@redhat.com>]

They are wrappers of POSIX fcntl "file private locking".

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 include/qemu/osdep.h |  2 ++
 util/osdep.c         | 31 +++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 1e3221c..81913a7 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -265,6 +265,8 @@ int qemu_madvise(void *addr, size_t len, int advice);
 
 int qemu_open(const char *name, int flags, ...);
 int qemu_close(int fd);
+int qemu_lock_fd(int fd, int64_t start, int64_t len, bool exclusive);
+int qemu_unlock_fd(int fd, int64_t start, int64_t len);
 
 #if defined(__HAIKU__) && defined(__i386__)
 #define FMT_pid "%ld"
diff --git a/util/osdep.c b/util/osdep.c
index d56d071..9e5d7fa 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -236,6 +236,37 @@ int qemu_close(int fd)
     return close(fd);
 }
 
+static int qemu_lock_fcntl(int fd, int64_t start, int64_t len, int fl_type)
+{
+#ifdef F_OFD_SETLK
+    struct flock fl = (struct flock) {
+        .l_whence  = SEEK_SET,
+        /* Locking byte 1 avoids interfereing with virtlockd. */
+        .l_start = start,
+        .l_len = len,
+        .l_type = fl_type,
+    };
+    if (fcntl(fd, F_OFD_SETLK, &fl) == -1) {
+        return -errno;
+    } else {
+        return 0;
+    }
+#else
+    return -ENOTSUP;
+#endif
+}
+
+int qemu_lock_fd(int fd, int64_t start, int64_t len, bool exclusive)
+{
+
+    return qemu_lock_fcntl(fd, start, len, exclusive ? F_WRLCK : F_RDLCK);
+}
+
+int qemu_unlock_fd(int fd, int64_t start, int64_t len)
+{
+    return qemu_lock_fcntl(fd, start, len, F_UNLCK);
+}
+
 /*
  * A variant of write(2) which handles partial write.
  *
-- 
2.8.2