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Refactor file locking, lifting the flock wrapper code into separate

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functions. Also fixes a bug, where a nonblocking lock could, in certain race
situations, succeed without actually obtaining the lock.
This commit is contained in:
Petr Rockai 2009-08-13 13:23:51 +00:00
parent 004c103c20
commit 5d5e2bf8f6
2 changed files with 71 additions and 54 deletions
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1
WHATS_NEW
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@ -1,5 +1,6 @@
Version 2.02.52 -
=================================
Fix bug where non-blocking file locks could be granted in error.
Make lvm2app pv_t, lv_t, vg_t handle definitions consistent with lvm_t.
Fix vgextend error path - if ORPHAN lock fails, unlock / release vg (2.02.49).
Fix compile warning in clvmd.

120
lib/locking/file_locking.c
View File

@ -43,13 +43,26 @@ static sig_t _oldhandler;
static sigset_t _fullsigset, _intsigset;
static volatile sig_atomic_t _handler_installed;
static void _undo_flock(const char *file, int fd)
{
struct stat buf1, buf2;
if (!flock(fd, LOCK_NB | LOCK_EX) &&
!stat(file, &buf1) &&
!fstat(fd, &buf2) &&
is_same_inode(buf1, buf2))
if (unlink(file))
log_sys_error("unlink", file);
if (close(fd) < 0)
log_sys_error("close", file);
}
static int _release_lock(const char *file, int unlock)
{
struct lock_list *ll;
struct dm_list *llh, *llt;
struct stat buf1, buf2;
dm_list_iterate_safe(llh, llt, &_lock_list) {
ll = dm_list_item(llh, struct lock_list);
@ -61,15 +74,7 @@ static int _release_lock(const char *file, int unlock)
log_sys_error("flock", ll->res);
}
if (!flock(ll->lf, LOCK_NB | LOCK_EX) &&
!stat(ll->res, &buf1) &&
!fstat(ll->lf, &buf2) &&
is_same_inode(buf1, buf2))
if (unlink(ll->res))
log_sys_error("unlink", ll->res);
if (close(ll->lf) < 0)
log_sys_error("close", ll->res);
_undo_flock(ll->res, ll->lf);
dm_free(ll->res);
dm_free(llh);
@ -124,14 +129,53 @@ static void _install_ctrl_c_handler()
siginterrupt(SIGINT, 1);
}
static int _do_flock(const char *file, int *fd, int operation, uint32_t nonblock)
{
int r = 1;
int old_errno;
struct stat buf1, buf2;
do {
if ((*fd > -1) && close(*fd))
log_sys_error("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
_install_ctrl_c_handler();
r = flock(*fd, operation);
old_errno = errno;
if (!nonblock)
_remove_ctrl_c_handler();
if (r) {
errno = old_errno;
log_sys_error("flock", file);
close(*fd);
return 0;
}
if (!stat(file, &buf1) && !fstat(*fd, &buf2) &&
is_same_inode(buf1, buf2))
return 1;
} while (!nonblock);
return_0;
}
static int _lock_file(const char *file, uint32_t flags)
{
int operation;
int r = 1;
int old_errno;
uint32_t nonblock = flags & LCK_NONBLOCK;
int r;
struct lock_list *ll;
struct stat buf1, buf2;
char state;
switch (flags & LCK_TYPE_MASK) {
@ -151,56 +195,28 @@ static int _lock_file(const char *file, uint32_t flags)
}
if (!(ll = dm_malloc(sizeof(struct lock_list))))
return 0;
return_0;
if (!(ll->res = dm_strdup(file))) {
dm_free(ll);
return 0;
return_0;
}
ll->lf = -1;
log_very_verbose("Locking %s %c%c", ll->res, state,
flags & LCK_NONBLOCK ? ' ' : 'B');
do {
if ((ll->lf > -1) && close(ll->lf))
log_sys_error("close", file);
if ((ll->lf = open(file, O_CREAT | O_APPEND | O_RDWR, 0777))
< 0) {
log_sys_error("open", file);
goto err;
}
if ((flags & LCK_NONBLOCK))
operation |= LOCK_NB;
else
_install_ctrl_c_handler();
r = flock(ll->lf, operation);
old_errno = errno;
if (!(flags & LCK_NONBLOCK))
_remove_ctrl_c_handler();
if (r) {
errno = old_errno;
log_sys_error("flock", ll->res);
close(ll->lf);
goto err;
}
if (!stat(ll->res, &buf1) && !fstat(ll->lf, &buf2) &&
is_same_inode(buf1, buf2))
break;
} while (!(flags & LCK_NONBLOCK));
nonblock ? ' ' : 'B');
r = _do_flock(file, &ll->lf, operation, nonblock);
if (r)
dm_list_add(&_lock_list, &ll->list);
return 1;
err:
else {
dm_free(ll->res);
dm_free(ll);
return 0;
stack;
}
return r;
}
static int _file_lock_resource(struct cmd_context *cmd, const char *resource,