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From 9d0247153a70ab1909d0690ec9b7f4d20e8cb602 Mon Sep 17 00:00:00 2001
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Message-Id: <9d0247153a70ab1909d0690ec9b7f4d20e8cb602@dist-git>
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From: Vasiliy Ulyanov <vulyanov@suse.de>
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Date: Wed, 2 Feb 2022 17:28:15 +0100
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Subject: [PATCH] virpidfile: Add virPidFileReadPathIfLocked func
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The function will attempt to read a pid from @path, and store it in
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@pid. The @pid will only be set, however, if @path is locked by
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virFileLock() at byte 0 and the pid in @path is running.
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Signed-off-by: Vasiliy Ulyanov <vulyanov@suse.de>
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Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
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Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
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(cherry picked from commit 013ab22f79d1345daf6b2778ca498acb16939011)
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Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2152188
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Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
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---
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src/libvirt_private.syms | 1 +
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src/util/virpidfile.c | 35 +++++++++++++++++++++++++++++++++++
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src/util/virpidfile.h | 2 ++
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3 files changed, 38 insertions(+)
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diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
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index fa734dfd33..568b0f34a1 100644
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--- a/src/libvirt_private.syms
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+++ b/src/libvirt_private.syms
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@@ -3061,6 +3061,7 @@ virPidFileRead;
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virPidFileReadIfAlive;
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virPidFileReadPath;
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virPidFileReadPathIfAlive;
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+virPidFileReadPathIfLocked;
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virPidFileRelease;
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virPidFileReleasePath;
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virPidFileWrite;
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diff --git a/src/util/virpidfile.c b/src/util/virpidfile.c
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index 7069f8343d..9d194f7336 100644
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--- a/src/util/virpidfile.c
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+++ b/src/util/virpidfile.c
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@@ -302,6 +302,41 @@ int virPidFileReadIfAlive(const char *dir,
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return 0;
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}
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+/**
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+ * virPidFileReadPathIfLocked:
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+ * @path: path to pidfile
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+ * @pid: variable to return pid in
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+ *
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+ * This will attempt to read a pid from @path, and store it in
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+ * @pid. The @pid will only be set, however, if the pid in @path
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+ * is running, and @path is locked by virFileLock() at byte 0
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+ * (which is exactly what virCommandSetPidFile() results in).
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+ * This adds protection against returning a stale pid.
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+ *
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+ * Returns -1 upon error, or zero on successful
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+ * reading of the pidfile. If @path is not locked
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+ * or if the PID was not still alive, zero will
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+ * be returned, but @pid will be set to -1.
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+ */
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+int virPidFileReadPathIfLocked(const char *path, pid_t *pid)
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+{
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+ VIR_AUTOCLOSE fd = -1;
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+
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+ if ((fd = open(path, O_RDWR)) < 0)
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+ return -1;
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+
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+ if (virFileLock(fd, false, 0, 1, false) >= 0) {
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+ /* The file isn't locked. PID is stale. */
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+ *pid = -1;
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+ return 0;
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+ }
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+
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+ if (virPidFileReadPathIfAlive(path, pid, NULL) < 0)
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+ return -1;
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+
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+ return 0;
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+}
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+
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int virPidFileDeletePath(const char *pidfile)
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{
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diff --git a/src/util/virpidfile.h b/src/util/virpidfile.h
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index fd8013c41e..e84542f298 100644
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--- a/src/util/virpidfile.h
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+++ b/src/util/virpidfile.h
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@@ -48,6 +48,8 @@ int virPidFileReadIfAlive(const char *dir,
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const char *name,
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pid_t *pid,
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const char *binpath) G_GNUC_WARN_UNUSED_RESULT;
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+int virPidFileReadPathIfLocked(const char *path,
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+ pid_t *pid) G_GNUC_WARN_UNUSED_RESULT;
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int virPidFileDeletePath(const char *path);
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int virPidFileDelete(const char *dir,
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--
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2.39.0
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