[PATCH] util: Rework virFileFlock() to be unambiguous

[Martin Kletzander]

The boolean parameters for lock/unlock and read/write (shared/exclusive) caused
a lot of confusion when reading the callers.  The new approach is explicit and
unambiguous.

While at it, also change the only caller so that it acquires an exclusive lock
as it should've been all the time.  This was caused because the function was
ambiguous since it was created in commit 5a0a5f7fb5f5, and due to that it was
misused in commit 657ddeff2313 and since then the lock being taken was shared
rather than exclusive.

Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
---
 src/util/virfile.c    | 27 ++++++++++++++++++---------
 src/util/virfile.h    |  9 ++++++++-
 src/util/virresctrl.c |  4 ++--
 3 files changed, 28 insertions(+), 12 deletions(-)

diff --git a/src/util/virfile.c b/src/util/virfile.c
index 213acdbcaa2b..554011eecb25 100644
--- a/src/util/virfile.c
+++ b/src/util/virfile.c
@@ -465,23 +465,33 @@ int virFileUnlock(int fd, off_t start, off_t len)
 /**
  * virFileFlock:
  * @fd: file descriptor to call flock on
- * @lock: true for lock, false for unlock
- * @shared: true if shared, false for exclusive, ignored if `@lock == false`
+ * @op: operation to perform
  *
  * This is just a simple wrapper around flock(2) that errors out on unsupported
  * platforms.
  *
  * The lock will be released when @fd is closed or this function is called with
- * `@lock == false`.
+ * `@op == VIR_FILE_FLOCK_UNLOCK`.
  *
  * Returns 0 on success, -1 otherwise (with errno set)
  */
-int virFileFlock(int fd, bool lock, bool shared)
+int virFileFlock(int fd, virFileFlockOperation op)
 {
-    if (lock)
-        return flock(fd, shared ? LOCK_SH : LOCK_EX);
+    int flock_op = -1;
 
-    return flock(fd, LOCK_UN);
+    switch (op) {
+    case VIR_FILE_FLOCK_SHARED:
+        flock_op = LOCK_SH;
+        break;
+    case VIR_FILE_FLOCK_EXCLUSIVE:
+        flock_op = LOCK_EX;
+        break;
+    case VIR_FILE_FLOCK_UNLOCK:
+        flock_op = LOCK_UN;
+        break;
+    }
+
+    return flock(fd, flock_op);
 }
 
 #else /* WIN32 */
@@ -505,8 +515,7 @@ int virFileUnlock(int fd G_GNUC_UNUSED,
 
 
 int virFileFlock(int fd G_GNUC_UNUSED,
-                 bool lock G_GNUC_UNUSED,
-                 bool shared G_GNUC_UNUSED)
+                 virFileFlockOperation op G_GNUC_UNUSED)
 {
     errno = ENOSYS;
     return -1;
diff --git a/src/util/virfile.h b/src/util/virfile.h
index 7a92364a5c9f..04428727fd3b 100644
--- a/src/util/virfile.h
+++ b/src/util/virfile.h
@@ -118,7 +118,14 @@ int virFileLock(int fd, bool shared, off_t start, off_t len, bool waitForLock)
 int virFileUnlock(int fd, off_t start, off_t len)
     G_GNUC_NO_INLINE;
 
-int virFileFlock(int fd, bool lock, bool shared);
+
+typedef enum {
+    VIR_FILE_FLOCK_EXCLUSIVE,
+    VIR_FILE_FLOCK_SHARED,
+    VIR_FILE_FLOCK_UNLOCK,
+} virFileFlockOperation;
+
+int virFileFlock(int fd, virFileFlockOperation op);
 
 typedef int (*virFileRewriteFunc)(int fd, const void *opaque);
 int virFileRewrite(const char *path,
diff --git a/src/util/virresctrl.c b/src/util/virresctrl.c
index 3563fc560db5..784a8d43bb2f 100644
--- a/src/util/virresctrl.c
+++ b/src/util/virresctrl.c
@@ -463,7 +463,7 @@ virResctrlLockWrite(void)
         return -1;
     }
 
-    if (virFileFlock(fd, true, true) < 0) {
+    if (virFileFlock(fd, VIR_FILE_FLOCK_EXCLUSIVE) < 0) {
         virReportSystemError(errno, "%s", _("Cannot lock resctrl"));
         VIR_FORCE_CLOSE(fd);
         return -1;
@@ -485,7 +485,7 @@ virResctrlUnlock(int fd)
         virReportSystemError(errno, "%s", _("Cannot close resctrl"));
 
         /* Trying to save the already broken */
-        if (virFileFlock(fd, false, false) < 0)
+        if (virFileFlock(fd, VIR_FILE_FLOCK_UNLOCK) < 0)
             virReportSystemError(errno, "%s", _("Cannot unlock resctrl"));
 
         return -1;
-- 
2.27.0