138 lines
4.0 KiB
C
138 lines
4.0 KiB
C
/* SPDX-License-Identifier: LGPL-2.1-or-later */
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#include <errno.h>
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#include <fcntl.h>
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#include <stdio.h>
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#include <string.h>
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#include <sys/file.h>
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#include <sys/stat.h>
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#include "alloc-util.h"
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#include "fd-util.h"
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#include "fs-util.h"
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#include "lockfile-util.h"
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#include "macro.h"
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#include "missing_fcntl.h"
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#include "path-util.h"
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int make_lock_file(const char *p, int operation, LockFile *ret) {
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_cleanup_close_ int fd = -1;
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_cleanup_free_ char *t = NULL;
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int r;
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/*
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* We use UNPOSIX locks if they are available. They have nice
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* semantics, and are mostly compatible with NFS. However,
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* they are only available on new kernels. When we detect we
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* are running on an older kernel, then we fall back to good
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* old BSD locks. They also have nice semantics, but are
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* slightly problematic on NFS, where they are upgraded to
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* POSIX locks, even though locally they are orthogonal to
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* POSIX locks.
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*/
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t = strdup(p);
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if (!t)
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return -ENOMEM;
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for (;;) {
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struct flock fl = {
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.l_type = (operation & ~LOCK_NB) == LOCK_EX ? F_WRLCK : F_RDLCK,
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.l_whence = SEEK_SET,
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};
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struct stat st;
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fd = open(p, O_CREAT|O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NOCTTY, 0600);
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if (fd < 0)
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return -errno;
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r = fcntl(fd, (operation & LOCK_NB) ? F_OFD_SETLK : F_OFD_SETLKW, &fl);
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if (r < 0) {
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/* If the kernel is too old, use good old BSD locks */
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if (errno == EINVAL)
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r = flock(fd, operation);
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if (r < 0)
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return errno == EAGAIN ? -EBUSY : -errno;
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}
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/* If we acquired the lock, let's check if the file
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* still exists in the file system. If not, then the
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* previous exclusive owner removed it and then closed
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* it. In such a case our acquired lock is worthless,
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* hence try again. */
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r = fstat(fd, &st);
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if (r < 0)
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return -errno;
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if (st.st_nlink > 0)
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break;
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fd = safe_close(fd);
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}
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ret->path = t;
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ret->fd = fd;
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ret->operation = operation;
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fd = -1;
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t = NULL;
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return r;
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}
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int make_lock_file_for(const char *p, int operation, LockFile *ret) {
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const char *fn;
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char *t;
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assert(p);
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assert(ret);
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fn = basename(p);
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if (!filename_is_valid(fn))
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return -EINVAL;
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t = newa(char, strlen(p) + 2 + 4 + 1);
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stpcpy(stpcpy(stpcpy(mempcpy(t, p, fn - p), ".#"), fn), ".lck");
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return make_lock_file(t, operation, ret);
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}
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void release_lock_file(LockFile *f) {
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int r;
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if (!f)
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return;
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if (f->path) {
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/* If we are the exclusive owner we can safely delete
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* the lock file itself. If we are not the exclusive
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* owner, we can try becoming it. */
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if (f->fd >= 0 &&
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(f->operation & ~LOCK_NB) == LOCK_SH) {
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static const struct flock fl = {
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.l_type = F_WRLCK,
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.l_whence = SEEK_SET,
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};
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r = fcntl(f->fd, F_OFD_SETLK, &fl);
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if (r < 0 && errno == EINVAL)
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r = flock(f->fd, LOCK_EX|LOCK_NB);
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if (r >= 0)
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f->operation = LOCK_EX|LOCK_NB;
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}
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if ((f->operation & ~LOCK_NB) == LOCK_EX)
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unlink_noerrno(f->path);
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f->path = mfree(f->path);
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}
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f->fd = safe_close(f->fd);
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f->operation = 0;
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}
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