From: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
In daemons using pidfiles to protect against concurrent
execution there is a possibility that a crash may leave a stale
pidfile on disk, which then prevents later restart of the daemon.
To avoid this problem, introduce a pair of APIs which make
use of virFileLock to ensure crash-safe & race condition-safe
pidfile acquisition & releae
* src/libvirt_private.syms, src/util/virpidfile.c,
src/util/virpidfile.h: Add virPidFileAcquire and virPidFileRelease
---
po/POTFILES.in | 1 +
src/libvirt_private.syms | 4 +
src/util/virpidfile.c | 142 ++++++++++++++++++++++++++++++++++++++++++++++
src/util/virpidfile.h | 12 ++++
4 files changed, 159 insertions(+), 0 deletions(-)
diff --git a/po/POTFILES.in b/po/POTFILES.in
index 7bb08b0..b200f89 100644
--- a/po/POTFILES.in
+++ b/po/POTFILES.in
@@ -123,6 +123,7 @@ src/util/sysinfo.c
src/util/util.c
src/util/viraudit.c
src/util/virfile.c
+src/util/virpidfile.c
src/util/virterror.c
src/util/xml.c
src/vbox/vbox_MSCOMGlue.c
diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
index fee3520..64b91ee 100644
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@@ -1120,11 +1120,15 @@ virFileFdopen;
# virpidfile.h
+virPidFileAcquire;
+virPidFileAcquirePath;
virPidFileBuildPath;
virPidFileRead;
virPidFileReadIfAlive;
virPidFileReadPath;
virPidFileReadPathIfAlive;
+virPidFileRelease;
+virPidFileReleasePath;
virPidFileWrite;
virPidFileWritePath;
virPidFileDelete;
diff --git a/src/util/virpidfile.c b/src/util/virpidfile.c
index dc92868..005c95d 100644
--- a/src/util/virpidfile.c
+++ b/src/util/virpidfile.c
@@ -25,11 +25,15 @@
#include <fcntl.h>
#include <signal.h>
+#include <sys/stat.h>
#include "virpidfile.h"
#include "virfile.h"
#include "memory.h"
#include "util.h"
+#include "intprops.h"
+#include "logging.h"
+#include "virterror_internal.h"
char *virPidFileBuildPath(const char *dir, const char* name)
@@ -255,3 +259,141 @@ cleanup:
VIR_FREE(pidfile);
return rc;
}
+
+
+
+int virPidFileAcquirePath(const char *path,
+ pid_t pid)
+{
+ int fd = -1;
+ char ebuf[1024];
+ char pidstr[INT_BUFSIZE_BOUND(pid)];
+ verify(sizeof(pid_t) <= sizeof(unsigned int));
+
+ if (path[0] == '\0')
+ return 0;
+
+ while (1) {
+ struct stat a, b;
+ if ((fd = open(path, O_WRONLY|O_CREAT, 0644)) < 0) {
+ VIR_ERROR(_("Failed to open pid file '%s' : %s"),
+ path, virStrerror(errno, ebuf, sizeof ebuf));
+ return -1;
+ }
+
+ if (fstat(fd, &b) < 0) {
+ VIR_ERROR(_("Unable to check status of pid file '%s': %s"),
+ path, virStrerror(errno, ebuf, sizeof ebuf));
+ VIR_FORCE_CLOSE(fd);
+ return -1;
+ }
+
+ if (virFileLock(fd, false, 0, 1) < 0) {
+ VIR_ERROR(_("Failed to acquire pid file '%s' : %s"),
+ path, virStrerror(errno, ebuf, sizeof ebuf));
+ VIR_FORCE_CLOSE(fd);
+ return -1;
+ }
+
+ /* Now make sure the pidfile we locked is the same
+ * one that now exists on the filesystem
+ */
+ if (stat(path, &a) < 0) {
+ VIR_DEBUG("Pid file '%s' disappeared: %s",
+ path, virStrerror(errno, ebuf, sizeof ebuf));
+ VIR_FORCE_CLOSE(fd);
+ /* Someone else must be racing with us, so try agin */
+ continue;
+ }
+
+ if (a.st_ino == b.st_ino)
+ break;
+
+ VIR_DEBUG("Pid file '%s' was recreated", path);
+ VIR_FORCE_CLOSE(fd);
+ /* Someone else must be racing with us, so try agin */
+ }
+
+ snprintf(pidstr, sizeof(pidstr), "%u", (unsigned int)pid);
+
+ if (safewrite(fd, pidstr, strlen(pidstr)) < 0) {
+ VIR_ERROR(_("Failed to write to pid file '%s' : %s"),
+ path, virStrerror(errno, ebuf, sizeof ebuf));
+ VIR_FORCE_CLOSE(fd);
+ }
+
+ return fd;
+}
+
+
+int virPidFileAcquire(const char *dir,
+ const char *name,
+ pid_t pid)
+{
+ int rc = 0;
+ char *pidfile = NULL;
+
+ if (name == NULL || dir == NULL) {
+ rc = -EINVAL;
+ goto cleanup;
+ }
+
+ if (!(pidfile = virPidFileBuildPath(dir, name))) {
+ rc = -ENOMEM;
+ goto cleanup;
+ }
+
+ rc = virPidFileAcquirePath(pidfile, pid);
+
+cleanup:
+ VIR_FREE(pidfile);
+ return rc;
+}
+
+
+int virPidFileReleasePath(const char *path,
+ int fd)
+{
+ int rc = 0;
+ /*
+ * We need to unlink before closing the FD to avoid
+ * a race, but Win32 won't let you unlink an open
+ * file handle. So on that platform we do the reverse
+ * and just have to live with the possible race.
+ */
+#ifdef WIN32
+ VIR_FORCE_CLOSE(fd);
+ if (unlink(path) < 0 && errno != ENOENT)
+ rc = -errno;
+#else
+ if (unlink(path) < 0 && errno != ENOENT)
+ rc = -errno;
+ VIR_FORCE_CLOSE(fd);
+#endif
+ return rc;
+}
+
+
+int virPidFileRelease(const char *dir,
+ const char *name,
+ int fd)
+{
+ int rc = 0;
+ char *pidfile = NULL;
+
+ if (name == NULL || dir == NULL) {
+ rc = -EINVAL;
+ goto cleanup;
+ }
+
+ if (!(pidfile = virPidFileBuildPath(dir, name))) {
+ rc = -ENOMEM;
+ goto cleanup;
+ }
+
+ rc = virPidFileReleasePath(pidfile, fd);
+
+cleanup:
+ VIR_FREE(pidfile);
+ return rc;
+}
diff --git a/src/util/virpidfile.h b/src/util/virpidfile.h
index 6659f1c..dc44fc9 100644
--- a/src/util/virpidfile.h
+++ b/src/util/virpidfile.h
@@ -55,4 +55,16 @@ int virPidFileDelete(const char *dir,
const char *name);
+int virPidFileAcquirePath(const char *path,
+ pid_t pid) ATTRIBUTE_RETURN_CHECK;
+int virPidFileAcquire(const char *dir,
+ const char *name,
+ pid_t pid) ATTRIBUTE_RETURN_CHECK;
+
+int virPidFileReleasePath(const char *path,
+ int fd);
+int virPidFileRelease(const char *dir,
+ const char *name,
+ int fd);
+
#endif /* __VIR_PIDFILE_H__ */
--
1.7.6
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