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lvm2/lib/misc/lvm-flock.c
2024-05-08 01:55:21 +02:00

256 lines
5.4 KiB
C

/*
* Copyright (C) 2001-2004 Sistina Software, Inc. All rights reserved.
* Copyright (C) 2004-2014 Red Hat, Inc. All rights reserved.
*
* This file is part of LVM2.
*
* This copyrighted material is made available to anyone wishing to use,
* modify, copy, or redistribute it subject to the terms and conditions
* of the GNU Lesser General Public License v.2.1.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program; if not, write to the Free Software Foundation,
* Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "lib/misc/lib.h"
#include "lib/config/config.h"
#include "lib/misc/lvm-flock.h"
#include "lib/misc/lvm-signal.h"
#include "lib/locking/locking.h"
#include <sys/file.h>
#include <fcntl.h>
struct lock_list {
struct dm_list list;
int lf;
char *res;
};
static struct dm_list _lock_list;
static int _prioritise_write_locks;
/* Drop lock known to be shared with another file descriptor. */
static void _drop_shared_flock(const char *file, int fd)
{
log_debug_locking("_drop_shared_flock %s.", file);
if (close(fd) < 0)
log_sys_debug("close", file);
}
static void _undo_flock(const char *file, int fd)
{
struct stat buf1, buf2;
log_debug_locking("_undo_flock %s", file);
if (!flock(fd, LOCK_NB | LOCK_EX) &&
!stat(file, &buf1) &&
!fstat(fd, &buf2) &&
is_same_inode(buf1, buf2))
if (unlink(file) && (errno != ENOENT))
log_sys_debug("unlink", file);
if (close(fd) < 0)
log_sys_debug("close", file);
}
static struct lock_list *_get_lock_list_entry(const char *file)
{
struct lock_list *ll;
struct dm_list *llh;
dm_list_iterate(llh, &_lock_list) {
ll = dm_list_item(llh, struct lock_list);
if (!strcmp(ll->res, file))
return ll;
}
return NULL;
}
static int _release_lock(const char *file, int unlock)
{
struct lock_list *ll;
struct dm_list *llh, *llt;
dm_list_iterate_safe(llh, llt, &_lock_list) {
ll = dm_list_item(llh, struct lock_list);
if (!file || !strcmp(ll->res, file)) {
dm_list_del(llh);
if (unlock) {
log_very_verbose("Unlocking %s", ll->res);
if (flock(ll->lf, LOCK_NB | LOCK_UN))
log_sys_debug("flock", ll->res);
_undo_flock(ll->res, ll->lf);
} else
_drop_shared_flock(ll->res, ll->lf);
free(ll->res);
free(llh);
if (file)
return 1;
}
}
return 0;
}
void release_flocks(int unlock)
{
_release_lock(NULL, unlock);
}
static int _do_flock(const char *file, int *fd, int operation, uint32_t nonblock)
{
int r;
int old_errno;
struct stat buf1, buf2;
log_debug_locking("_do_flock %s %c%c", file,
operation == LOCK_EX ? 'W' : 'R', nonblock ? ' ' : 'B');
do {
if ((*fd > -1) && close(*fd))
log_sys_debug("close", file);
if ((*fd = open(file, O_CREAT | O_APPEND | O_RDWR, 0777)) < 0) {
log_sys_error("open", file);
return 0;
}
if (nonblock)
operation |= LOCK_NB;
else
sigint_allow();
r = flock(*fd, operation);
old_errno = errno;
if (!nonblock) {
sigint_restore();
if (sigint_caught()) {
log_error("Giving up waiting for lock.");
break;
}
}
if (r) {
errno = old_errno;
log_sys_error("flock", file);
break;
}
if (!stat(file, &buf1) && !fstat(*fd, &buf2) &&
is_same_inode(buf1, buf2))
return 1;
} while (!nonblock);
if (close(*fd))
log_sys_debug("close", file);
*fd = -1;
return_0;
}
#define AUX_LOCK_SUFFIX ":aux"
static int _do_write_priority_flock(const char *file, int *fd, int operation, uint32_t nonblock)
{
int r, fd_aux = -1;
char file_aux[PATH_MAX];
snprintf(file_aux, sizeof(file_aux), "%s%s", file, AUX_LOCK_SUFFIX);
if ((r = _do_flock(file_aux, &fd_aux, LOCK_EX, nonblock))) {
if (operation == LOCK_EX) {
r = _do_flock(file, fd, operation, nonblock);
_undo_flock(file_aux, fd_aux);
} else {
_undo_flock(file_aux, fd_aux);
r = _do_flock(file, fd, operation, nonblock);
}
}
return r;
}
int lock_file(const char *file, uint32_t flags)
{
int operation;
uint32_t nonblock = flags & LCK_NONBLOCK;
uint32_t convert = flags & LCK_CONVERT;
int r;
struct lock_list *ll;
char state;
switch (flags & LCK_TYPE_MASK) {
case LCK_READ:
operation = LOCK_SH;
state = 'R';
break;
case LCK_WRITE:
operation = LOCK_EX;
state = 'W';
break;
case LCK_UNLOCK:
return _release_lock(file, 1);
default:
log_error("Unrecognised lock type: %d", flags & LCK_TYPE_MASK);
return 0;
}
if (convert) {
if (nonblock)
operation |= LOCK_NB;
if (!(ll = _get_lock_list_entry(file)))
return 0;
log_very_verbose("Locking %s %c%c convert", ll->res, state,
nonblock ? ' ' : 'B');
r = flock(ll->lf, operation);
if (!r)
return 1;
log_error("Failed to convert flock on %s %d", file, errno);
return 0;
}
if (!(ll = malloc(sizeof(struct lock_list))))
return_0;
if (!(ll->res = strdup(file))) {
free(ll);
return_0;
}
ll->lf = -1;
log_very_verbose("Locking %s %c%c", ll->res, state,
nonblock ? ' ' : 'B');
(void) dm_prepare_selinux_context(file, S_IFREG);
if (_prioritise_write_locks)
r = _do_write_priority_flock(file, &ll->lf, operation, nonblock);
else
r = _do_flock(file, &ll->lf, operation, nonblock);
(void) dm_prepare_selinux_context(NULL, 0);
if (r)
dm_list_add(&_lock_list, &ll->list);
else {
free(ll->res);
free(ll);
stack;
}
return r;
}
void init_flock(struct cmd_context *cmd)
{
dm_list_init(&_lock_list);
_prioritise_write_locks =
find_config_tree_bool(cmd, global_prioritise_write_locks_CFG, NULL);
}