[ovs-dev] [PATCH V7] windows: Added lockf function and lock PID file

[Paul Boca]

If the PID file isn't locked then appctl.py detects it as stale and
bails out without doing anything. Because of this lots of Python tests fail.
Also this protects the PID file from being overwritten.

I used only shared lock, in order to be compatible with Python tests,
which try to acquire the lock exclusively. On Windows if the exclusive lock
is used, than the read access is denied too for other instances of this file.

Signed-off-by: Paul-Daniel Boca <pboca at cloudbasesolutions.com>
---
V2: No changes
V3: No changes
V4: No changes
V5: Removed this patch from Python series.
    Removed unused constants and defined 0xFFFF0000 as constant.
    Updated commit text.
V6: flock returns now the error of GetLastError.
    Also it uses fd parameter instead of the global filep_pidfile.
    Removed unused local variable and unnecessary error message.
V7: Keep a shared lock on PID file after the fopen.
    This ensures us that at most one process can write the same PID file.
    fopen with 'w' on Windows creates a file with FILE_SHARED_WRITE
    flag, so anyone with write access on file can write it.
---
 lib/daemon-windows.c | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/lib/daemon-windows.c b/lib/daemon-windows.c
index 8cf0fea..e6e1452 100644
--- a/lib/daemon-windows.c
+++ b/lib/daemon-windows.c
@@ -18,6 +18,7 @@
 #include "daemon.h"
 #include "daemon-private.h"
 #include <stdio.h>
+#include <io.h>
 #include <stdlib.h>
 #include "dirs.h"
 #include "ovs-thread.h"
@@ -26,6 +27,14 @@
 
 VLOG_DEFINE_THIS_MODULE(daemon_windows);
 
+/* Constants for flock function */
+#define	LOCK_SH	0x0                         /* Shared lock. */
+#define	LOCK_EX	LOCKFILE_EXCLUSIVE_LOCK     /* Exclusive lock. */
+#define	LOCK_UN	0x80000000                  /* Unlock. Custom value. */
+
+/* High-order 32 bits of byte range to lock */
+#define LOCK_MAX_SIZE 0xFFFF0000
+
 static bool service_create;          /* Was --service specified? */
 static bool service_started;         /* Have we dispatched service to start? */
 
@@ -404,9 +413,35 @@ detach_process(int argc, char *argv[])
 }
 
 static void
+flock(FILE* fd, int operation)
+{
+    HANDLE hFile;
+    OVERLAPPED ov = {0};
+
+    hFile = (HANDLE)_get_osfhandle(fileno(fd));
+    if (hFile == INVALID_HANDLE_VALUE) {
+        VLOG_FATAL("Invalid handle value");
+    }
+
+    if (operation & LOCK_UN) {
+        if (UnlockFileEx(hFile, 0, 0, LOCK_MAX_SIZE, &ov) == 0) {
+            VLOG_FATAL("Failed to unlock PID file (%s).",
+                       ovs_lasterror_to_string());
+        }
+    } else {
+        if (LockFileEx(hFile, operation, 0, 0, LOCK_MAX_SIZE, &ov) == FALSE) {
+            VLOG_FATAL("Failed to lock PID file (%s).",
+                       ovs_lasterror_to_string());
+        }
+    }
+}
+
+static void
 unlink_pidfile(void)
 {
     if (filep_pidfile) {
+        /* Remove the shared lock on file */
+        flock(filep_pidfile, LOCK_UN);
         fclose(filep_pidfile);
     }
     if (pidfile) {
@@ -437,6 +472,8 @@ make_pidfile(void)
         VLOG_FATAL("failed to open %s (%s)", pidfile, ovs_strerror(errno));
     }
 
+    flock(filep_pidfile, LOCK_EX);
+
     fatal_signal_add_hook(unlink_pidfile, NULL, NULL, true);
 
     fprintf(filep_pidfile, "%d\n", _getpid());
@@ -444,6 +481,10 @@ make_pidfile(void)
         VLOG_FATAL("Failed to write into the pidfile %s", pidfile);
     }
 
+    flock(filep_pidfile, LOCK_SH);
+    /* This will remove the exclusive lock. The shared lock will remain */
+    flock(filep_pidfile, LOCK_UN);
+
     /* Don't close the pidfile till the process exits. */
 }
 
-- 
2.7.2.windows.1