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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 15:35:18 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-07 15:35:18 +0000 |
commit | b750101eb236130cf056c675997decbac904cc49 (patch) | |
tree | a5df1a06754bdd014cb975c051c83b01c9a97532 /src/shared/lockfile-util.c | |
parent | Initial commit. (diff) | |
download | systemd-upstream.tar.xz systemd-upstream.zip |
Adding upstream version 252.22.upstream/252.22upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to '')
-rw-r--r-- | src/shared/lockfile-util.c | 137 |
1 files changed, 137 insertions, 0 deletions
diff --git a/src/shared/lockfile-util.c b/src/shared/lockfile-util.c new file mode 100644 index 0000000..6f059ab --- /dev/null +++ b/src/shared/lockfile-util.c @@ -0,0 +1,137 @@ +/* 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 "lockfile-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 = -1; + _cleanup_free_ char *t = NULL; + int r; + + /* + * We use UNPOSIX locks if they are available. They have nice + * semantics, and are mostly compatible with NFS. However, + * they are only available on new kernels. When we detect we + * are running on an older kernel, then we fall back to good + * old BSD locks. They also have nice semantics, but are + * slightly problematic on NFS, where they are upgraded to + * POSIX locks, even though locally they are orthogonal to + * POSIX locks. + */ + + 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; + + r = fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl); + if (r < 0) { + + /* If the kernel is too old, use good old BSD locks */ + if (errno == EINVAL) + r = flock(fd, operation); + + if (r < 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. */ + + r = fstat(fd, &st); + if (r < 0) + return -errno; + if (st.st_nlink > 0) + break; + + fd = safe_close(fd); + } + + ret->path = t; + ret->fd = fd; + ret->operation = operation; + + fd = -1; + t = NULL; + + return r; +} + +int make_lock_file_for(const char *p, int operation, LockFile *ret) { + const char *fn; + char *t; + + assert(p); + assert(ret); + + fn = basename(p); + if (!filename_is_valid(fn)) + return -EINVAL; + + t = newa(char, strlen(p) + 2 + 4 + 1); + stpcpy(stpcpy(stpcpy(mempcpy(t, p, fn - p), ".#"), fn), ".lck"); + + return make_lock_file(t, operation, ret); +} + +void release_lock_file(LockFile *f) { + int r; + + 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, + }; + + r = fcntl(f->fd, F_OFD_SETLK, &fl); + if (r < 0 && errno == EINVAL) + r = flock(f->fd, LOCK_EX|LOCK_NB); + + if (r >= 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; +} |