lock-util: Move to src/basic

src/basic/lock-util.c

@@ -0,0 +1,161 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+
+#include "alloc-util.h"
+#include "fd-util.h"
+#include "fs-util.h"
+#include "lock-util.h"
+#include "macro.h"
+#include "missing_fcntl.h"
+#include "path-util.h"
+
+int make_lock_file(const char *p, int operation, LockFile *ret) {
+        _cleanup_close_ int fd = -EBADF;
+        _cleanup_free_ char *t = NULL;
+
+        assert(p);
+        assert(ret);
+
+        /* We use UNPOSIX locks as they have nice semantics, and are mostly compatible with NFS. */
+
+        t = strdup(p);
+        if (!t)
+                return -ENOMEM;
+
+        for (;;) {
+                struct flock fl = {
+                        .l_type = (operation & ~LOCK_NB) == LOCK_EX ? F_WRLCK : F_RDLCK,
+                        .l_whence = SEEK_SET,
+                };
+                struct stat st;
+
+                fd = open(p, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600);
+                if (fd < 0)
+                        return -errno;
+
+                if (fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl) < 0)
+                        return errno == EAGAIN ? -EBUSY : -errno;
+
+                /* If we acquired the lock, let's check if the file still exists in the file system. If not,
+                 * then the previous exclusive owner removed it and then closed it. In such a case our
+                 * acquired lock is worthless, hence try again. */
+
+                if (fstat(fd, &st) < 0)
+                        return -errno;
+                if (st.st_nlink > 0)
+                        break;
+
+                fd = safe_close(fd);
+        }
+
+        *ret = (LockFile) {
+                .path = TAKE_PTR(t),
+                .fd = TAKE_FD(fd),
+                .operation = operation,
+        };
+
+        return 0;
+}
+
+int make_lock_file_for(const char *p, int operation, LockFile *ret) {
+        _cleanup_free_ char *fn = NULL, *dn = NULL, *t = NULL;
+        int r;
+
+        assert(p);
+        assert(ret);
+
+        r = path_extract_filename(p, &fn);
+        if (r < 0)
+                return r;
+
+        r = path_extract_directory(p, &dn);
+        if (r < 0)
+                return r;
+
+        t = strjoin(dn, "/.#", fn, ".lck");
+        if (!t)
+                return -ENOMEM;
+
+        return make_lock_file(t, operation, ret);
+}
+
+void release_lock_file(LockFile *f) {
+        if (!f)
+                return;
+
+        if (f->path) {
+
+                /* If we are the exclusive owner we can safely delete
+                 * the lock file itself. If we are not the exclusive
+                 * owner, we can try becoming it. */
+
+                if (f->fd >= 0 &&
+                    (f->operation & ~LOCK_NB) == LOCK_SH) {
+                        static const struct flock fl = {
+                                .l_type = F_WRLCK,
+                                .l_whence = SEEK_SET,
+                        };
+
+                        if (fcntl(f->fd, F_OFD_SETLK, &fl) >= 0)
+                                f->operation = LOCK_EX|LOCK_NB;
+                }
+
+                if ((f->operation & ~LOCK_NB) == LOCK_EX)
+                        unlink_noerrno(f->path);
+
+                f->path = mfree(f->path);
+        }
+
+        f->fd = safe_close(f->fd);
+        f->operation = 0;
+}
+
+int unposix_lock(int fd, int operation) {
+        int cmd, type, r;
+
+        assert(fd >= 0);
+
+        cmd = (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW;
+
+        switch (operation & ~LOCK_NB) {
+                case LOCK_EX:
+                        type = F_WRLCK;
+                        break;
+                case LOCK_SH:
+                        type = F_RDLCK;
+                        break;
+                case LOCK_UN:
+                        type = F_UNLCK;
+                        break;
+                default:
+                        assert_not_reached();
+        }
+
+        r = RET_NERRNO(fcntl(fd, cmd, &(struct flock) {
+                .l_type = type,
+                .l_whence = SEEK_SET,
+                .l_start = 0,
+                .l_len = 0,
+        }));
+
+        if (r == -EACCES) /* Treat EACCESS/EAGAIN the same as per man page. */
+                r = -EAGAIN;
+
+        return r;
+}
+
+void unposix_unlockpp(int **fd) {
+        assert(fd);
+
+        if (!*fd || **fd < 0)
+                return;
+
+        (void) unposix_lock(**fd, LOCK_UN);
+        *fd = NULL;
+}

src/basic/lock-util.h

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+typedef struct LockFile {
+        char *path;
+        int fd;
+        int operation;
+} LockFile;
+
+int make_lock_file(const char *p, int operation, LockFile *ret);
+int make_lock_file_for(const char *p, int operation, LockFile *ret);
+void release_lock_file(LockFile *f);
+
+#define LOCK_FILE_INIT { .fd = -EBADF, .path = NULL }
+
+/* Open File Description locks with the same interface as flock(). */
+int unposix_lock(int fd, int operation);
+
+void unposix_unlockpp(int **fd);
+
+#define CLEANUP_UNPOSIX_UNLOCK(fd)                                   \
+        _cleanup_(unposix_unlockpp) _unused_ int *CONCATENATE(_cleanup_unposix_unlock_, UNIQ) = &(fd)

src/basic/meson.build

@@ -46,6 +46,7 @@ basic_sources = files(
         'ioprio-util.c',
         'limits-util.c',
         'locale-util.c',
+        'lock-util.c',
         'log.c',
         'login-util.c',
         'memfd-util.c',