src/lxc/lxclock.h

   1 /* liblxcapi
   2  *
   3  * Copyright © 2012 Serge Hallyn <serge.hallyn@ubuntu.com>.
   4  * Copyright © 2012 Canonical Ltd.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2, as
   8  * published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  */
  19
  20 #include <fcntl.h>           /* For O_* constants */
  21 #include <sys/stat.h>        /* For mode constants */
  22 #include <sys/file.h>
  23 #include <semaphore.h>
  24 #include <string.h>
  25 #include <time.h>
  26
  27 #define LXC_LOCK_ANON_SEM 1
  28 #define LXC_LOCK_FLOCK 2
  29 struct lxc_lock {
  30         short type;
  31         union {
  32                 sem_t *sem; // an anonymous semaphore
  33                 struct {
  34                         int fd; // fd on which a lock is held (if not -1)
  35                         char *fname;
  36                 } f;
  37         } u;
  38 };
  39
  40 /*
  41  * lxc_newlock: Create a new (unlocked) lock.
  42  *
  43  * if name is not given, create an unnamed semaphore.  We use these
  44  * to protect against racing threads.
  45  * Note that an unnamed sem was malloced by us and needs to be freed.
  46  *
  47  * sem is initialized to value of 1
  48  * A sem_t * which can be passed to lxclock() and lxcunlock()
  49  * will be placed in l->u.sem
  50  *
  51  * If lxcpath and name are given (both must be given if either is
  52  * given) then a lockfile is created, $lxcpath/$lxcname/locks/$name.
  53  * We use that to protect the containers as represented on disk.
  54  * lxc_newlock() for the named lock only allocates the pathname in
  55  * memory so we can quickly open+lock it at lxclock.
  56  * l->u.f.fname will container the malloc'ed name (which must be
  57  * freed when the container is freed), and u.f.fd = -1.
  58  *
  59  * return lxclock on success, NULL on failure.
  60  */
  61 extern struct lxc_lock *lxc_newlock(const char *lxcpath, const char *name);
  62
  63 /*
  64  * lxclock: take an existing lock.  If timeout is 0, wait
  65  * indefinately.  Otherwise use given timeout.
  66  * return 0 if we got the lock, -2 on failure to set timeout, or -1
  67  * otherwise in which case errno will be set by sem_wait()).
  68  *
  69  * Note that timeout is (currently?) only supported for privlock, not
  70  * for slock.  Since currently there is not a single use of the timeout
  71  * (except in the test case) I may remove the support for it in sem as
  72  * well.
  73  */
  74 extern int lxclock(struct lxc_lock *lock, int timeout);
  75
  76 /*
  77  * lxcunlock: unlock given sem.  Return 0 on success, or -2 if we did not
  78  * have the lock.  Otherwise returns -1 with errno saved from flock
  79  * or sem_post function.
  80  */
  81 extern int lxcunlock(struct lxc_lock *lock);
  82
  83 extern void lxc_putlock(struct lxc_lock *l);