216 lines
6.1 KiB
Diff
216 lines
6.1 KiB
Diff
From 2e22136c0ef7fd5744460d783ef570525df42337 Mon Sep 17 00:00:00 2001
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From: Karel Zak <kzak@redhat.com>
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Date: Mon, 22 Jan 2024 12:56:24 +0100
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Subject: libmount: add utab.act file
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The file exists when libmount works with utab, and more steps are
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expected during a single mount operation (more kernel events, more
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updates to utab, etc.).
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It is possible to monitor the file through the mnt_monitor_...() API
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by a simple access() after any event. No locks are expected in
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monitor, making it usable for non-root users without any security
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impact. The monitor can ignore events if the file exist.
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Addresses: https://issues.redhat.com/browse/RHEL-14612
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Upstream: http://github.com/util-linux/util-linux/commit/9218c9678a6aa9b163705364246ed128e94fabb7
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Signed-off-by: Karel Zak <kzak@redhat.com>
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---
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libmount/src/context.c | 7 +++
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libmount/src/mountP.h | 2 +
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libmount/src/tab_update.c | 109 ++++++++++++++++++++++++++++++++++++++
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3 files changed, 118 insertions(+)
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diff --git a/libmount/src/context.c b/libmount/src/context.c
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index 06ac50dc2..27e06a19c 100644
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--- a/libmount/src/context.c
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+++ b/libmount/src/context.c
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@@ -2261,6 +2261,10 @@ int mnt_context_prepare_update(struct libmnt_context *cxt)
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rc = mnt_update_set_fs(cxt->update, cxt->mountflags,
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NULL, cxt->fs);
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+ if (mnt_update_is_ready(cxt->update)) {
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+ DBG(CXT, ul_debugobj(cxt, "update is ready"));
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+ mnt_update_start(cxt->update);
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+ }
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return rc < 0 ? rc : 0;
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}
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@@ -2319,7 +2323,10 @@ int mnt_context_update_tabs(struct libmnt_context *cxt)
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emit:
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if (rc == 0 && !mnt_context_within_helper(cxt))
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mnt_update_emit_event(cxt->update);
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+
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end:
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+ mnt_update_end(cxt->update);
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+
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if (!mnt_context_switch_ns(cxt, ns_old))
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return -MNT_ERR_NAMESPACE;
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return rc;
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diff --git a/libmount/src/mountP.h b/libmount/src/mountP.h
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index eddc82bde..505d70808 100644
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--- a/libmount/src/mountP.h
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+++ b/libmount/src/mountP.h
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@@ -478,6 +478,8 @@ extern int mnt_update_set_filename(struct libmnt_update *upd,
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const char *filename, int userspace_only);
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extern int mnt_update_emit_event(struct libmnt_update *upd);
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extern int mnt_update_already_done(struct libmnt_update *upd);
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+extern int mnt_update_start(struct libmnt_update *upd);
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+extern int mnt_update_end(struct libmnt_update *upd);
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#if __linux__
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/* btrfs.c */
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diff --git a/libmount/src/tab_update.c b/libmount/src/tab_update.c
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index 25a734e9d..7b088c025 100644
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--- a/libmount/src/tab_update.c
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+++ b/libmount/src/tab_update.c
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@@ -38,6 +38,9 @@ struct libmnt_update {
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unsigned long mountflags;
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int userspace_only;
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+ int act_fd;
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+ char *act_filename;
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+
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unsigned int ready : 1,
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missing_options : 1;
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@@ -61,6 +64,7 @@ struct libmnt_update *mnt_new_update(void)
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if (!upd)
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return NULL;
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+ upd->act_fd = -1;
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DBG(UPDATE, ul_debugobj(upd, "allocate"));
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return upd;
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}
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@@ -81,8 +85,11 @@ void mnt_free_update(struct libmnt_update *upd)
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mnt_unref_lock(upd->lock);
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mnt_unref_fs(upd->fs);
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mnt_unref_table(upd->mountinfo);
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+ if (upd->act_fd >= 0)
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+ close(upd->act_fd);
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free(upd->target);
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free(upd->filename);
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+ free(upd->act_filename);
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free(upd);
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}
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@@ -1004,6 +1011,8 @@ int mnt_update_emit_event(struct libmnt_update *upd)
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if (asprintf(&filename, "%s.event", upd->filename) <= 0)
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return -ENOMEM;
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+ DBG(UPDATE, ul_debugobj(upd, "emitting utab event"));
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+
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fd = open(filename, O_WRONLY|O_CREAT|O_CLOEXEC,
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S_IWUSR|S_IRUSR|S_IRGRP|S_IROTH);
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free(filename);
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@@ -1013,6 +1022,106 @@ int mnt_update_emit_event(struct libmnt_update *upd)
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return 0;
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}
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+/*
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+ * Let's use /run/mount/utab.act file to report to libmount monitor that
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+ * libmount is working with utab. In this case, the monitor can ignore all
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+ * events from kernel until entire mount (with all steps) is done.
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+ *
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+ * For example mount NFS with x-* options, means
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+ * - create utab.act and mark it as used (by LOCK_SH)
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+ * - exec /sbin/mount.nfs
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+ * - call mount(2) (kernel event on /proc/self/mounts)
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+ * - utab update (NFS stuff)
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+ * - utab update (add x-* userspace options)
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+ * - unlink utab.act (if not use anyone else)
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+ * - release event by /run/mount/utab.event
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+ *
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+ * Note, this is used only when utab is in the game (x-* options).
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+ */
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+int mnt_update_start(struct libmnt_update *upd)
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+{
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+ int rc = 0;
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+ mode_t oldmask;
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+
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+ if (!upd || !upd->filename)
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+ return -EINVAL;
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+
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+ if (!upd->act_filename &&
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+ asprintf(&upd->act_filename, "%s.act", upd->filename) <= 0)
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+ return -ENOMEM;
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+
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+ /* Use exclusive lock to avoid some other proces will remove the the
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+ * file before it's marked as used by LOCK_SH (below) */
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+ rc = update_init_lock(upd, NULL);
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+ if (rc)
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+ return rc;
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+
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+ rc = mnt_lock_file(upd->lock);
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+ if (rc)
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+ return -MNT_ERR_LOCK;
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+
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+ DBG(UPDATE, ul_debugobj(upd, "creating act file"));
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+
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+ oldmask = umask(S_IRGRP|S_IWGRP|S_IXGRP|S_IROTH|S_IWOTH|S_IXOTH);
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+ upd->act_fd = open(upd->act_filename, O_WRONLY|O_CREAT|O_CLOEXEC, S_IRUSR|S_IWUSR);
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+ umask(oldmask);
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+
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+ if (upd->act_fd < 0) {
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+ rc = -errno;
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+ goto fail;
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+ }
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+
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+ /* mark the file as used */
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+ rc = flock(upd->act_fd, LOCK_SH);
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+ if (rc) {
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+ rc = -errno;
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+ goto fail;
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+ }
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+
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+ mnt_unlock_file(upd->lock);
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+ return 0;
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+fail:
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+ DBG(UPDATE, ul_debugobj(upd, "act file failed [rc=%d]", rc));
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+ mnt_unlock_file(upd->lock);
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+ unlink(upd->act_filename);
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+ close(upd->act_fd);
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+ upd->act_fd = -1;
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+ return rc;
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+}
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+
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+int mnt_update_end(struct libmnt_update *upd)
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+{
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+ int rc;
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+
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+ if (!upd || upd->act_fd < 0)
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+ return -EINVAL;
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+
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+ DBG(UPDATE, ul_debugobj(upd, "removing act file"));
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+
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+ /* make sure nobody else will use the file */
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+ rc = mnt_lock_file(upd->lock);
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+ if (rc)
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+ return -MNT_ERR_LOCK;
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+
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+ /* mark the file as unused */
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+ flock(upd->act_fd, LOCK_UN);
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+ errno = 0;
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+
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+ /* check if nobody else need the file (if yes, then the file is under LOCK_SH) )*/
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+ if (flock(upd->act_fd, LOCK_EX | LOCK_NB) != 0) {
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+ if (errno == EWOULDBLOCK)
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+ DBG(UPDATE, ul_debugobj(upd, "act file used, no unlink"));
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+ } else {
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+ DBG(UPDATE, ul_debugobj(upd, "unlinking act file"));
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+ unlink(upd->act_filename);
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+ }
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+
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+ mnt_unlock_file(upd->lock);
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+ close(upd->act_fd);
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+ upd->act_fd = -1;
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+ return 0;
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+}
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+
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#ifdef TEST_PROGRAM
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static int update(const char *target, struct libmnt_fs *fs, unsigned long mountflags)
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--
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2.43.0
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