Re: [libvirt] [PATCH 4/5] Add some APIs which use locking for crashsafe pidfile handling

From: "Daniel P. Berrange" <berrange(a)redhat.com&gt; 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));