On 25 July 2016 at 05:50, Paul Boca <pb...@cloudbasesolutions.com> wrote:
> 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 <pb...@cloudbasesolutions.com>
> Acked-by: Alin Gabriel Serdean <aserd...@cloudbasesolutions.com>
>
Thank you, applied!
> ---
> 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.
> V8: Added LOCKFILE_FAIL_IMMEDIATELY flag when trying to get exclusive lock
> on PID file in order to avoid hangs of other daemons that try to
> acquire
> exclusive lock over the same PID file
> V9: Small fatal error message update and on constants used.
> Lock only the first byte in PID file, this is enough in our case.
> ---
> lib/daemon-windows.c | 41 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 41 insertions(+)
>
> diff --git a/lib/daemon-windows.c b/lib/daemon-windows.c
> index 8cf0fea..d77724e 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 +27,10 @@
>
> VLOG_DEFINE_THIS_MODULE(daemon_windows);
>
> +/* Constants for flock function */
> +#define LOCK_SHARED 0x0 /* Shared lock. */
> +#define LOCK_UNLOCK 0x80000000 /* Unlock. Custom
> value. */
> +
> static bool service_create; /* Was --service specified? */
> static bool service_started; /* Have we dispatched service to
> start? */
>
> @@ -404,9 +409,39 @@ 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("Failed to get PID file handle (%s).",
> + ovs_lasterror_to_string());
> + }
> +
> + if (operation & LOCK_UNLOCK) {
> + if (UnlockFileEx(hFile, 0, 1, 0, &ov) == 0) {
> + VLOG_FATAL("Failed to unlock PID file (%s).",
> + ovs_lasterror_to_string());
> + }
> + } else {
> + /* Use LOCKFILE_FAIL_IMMEDIATELY flag to avoid hang of another
> daemon that tries to
> + acquire exclusive lock over the same PID file */
> + if (LockFileEx(hFile, operation | LOCKFILE_FAIL_IMMEDIATELY,
> + 0, 1, 0, &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_UNLOCK);
> 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, LOCKFILE_EXCLUSIVE_LOCK);
> +
> 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_SHARED);
> + /* This will remove the exclusive lock. The shared lock will remain */
> + flock(filep_pidfile, LOCK_UNLOCK);
> +
> /* Don't close the pidfile till the process exits. */
> }
>
> --
> 2.7.2.windows.1
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