src/lxc/lxclock.h

   1 /*! \file
   2  *
   3  * liblxcapi
   4  *
   5  * Copyright © 2012 Serge Hallyn <serge.hallyn@ubuntu.com>.
   6  * Copyright © 2012 Canonical Ltd.
   7  *
   8  *  This library is free software; you can redistribute it and/or
   9  *  modify it under the terms of the GNU Lesser General Public
  10  *  License as published by the Free Software Foundation; either
  11  *  version 2.1 of the License, or (at your option) any later version.
  12  *
  13  *  This library is distributed in the hope that it will be useful,
  14  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  *  Lesser General Public License for more details.
  17  *
  18  *  You should have received a copy of the GNU Lesser General Public
  19  *  License along with this library; if not, write to the Free Software
  20  *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  21  */
  22
  23 #ifndef __LXC_LXCLOCK_H
  24 #define __LXC_LXCLOCK_H
  25
  26 #include <fcntl.h>           /* For O_* constants */
  27 #include <sys/stat.h>        /* For mode constants */
  28 #include <sys/file.h>
  29 #include <semaphore.h>
  30 #include <string.h>
  31 #include <time.h>
  32
  33 #define LXC_LOCK_ANON_SEM 1 /*!< Anonymous semaphore lock */
  34 #define LXC_LOCK_FLOCK    2 /*!< flock(2) lock */
  35
  36 // private
  37 /*!
  38  * LXC Lock
  39 */
  40 struct lxc_lock {
  41         short type; //!< Lock type
  42
  43         union {
  44                 sem_t *sem; //!< Anonymous semaphore (LXC_LOCK_ANON_SEM)
  45                 /*! LXC_LOCK_FLOCK details */
  46                 struct {
  47                         int   fd; //!< fd on which a lock is held (if not -1)
  48                         char *fname; //!< Name of lock
  49                 } f;
  50         } u; //!< Container for lock type elements
  51 };
  52
  53 /*!
  54  * \brief Create a new (unlocked) lock.
  55  *
  56  * \param lxcpath lxcpath lock should relate to.
  57  * \param name Name for lock.
  58  *
  59  * \return Newly-allocated lxclock on success, \c NULL on failure.
  60
  61  * \note If \p name is not given, create an unnamed semaphore
  62  *  (used to protect against racing threads).
  63  *
  64  * \note Note that an unnamed sem was malloced by us and needs to be freed.
  65  *
  66  * \internal \ref sem is initialized to a value of \c 1.
  67  * A 'sem_t *' which can be passed to \ref lxclock() and \ref lxcunlock()
  68  * will be placed in \c l->u.sem.
  69  *
  70  * If \ref lxcpath and \ref name are given (both must be given if either is
  71  * given) then a lockfile is created as \c /run/lxc/lock/$lxcpath/.$name if root,
  72  * or \c $XDG_RUNTIME_DIR/lxc/lock/$lxcpath/.$name if non-root.
  73  * The lock is used to protect the containers on-disk representation.
  74  *
  75  * \internal This function allocates the pathname for the given lock in memory
  76  * such that it can be can quickly opened and locked by \ref lxclock().
  77  * \c l->u.f.fname will contain the malloc'ed name (which must be
  78  * freed when the container is freed), and \c u.f.fd = -1.
  79  *
  80  */
  81 extern struct lxc_lock *lxc_newlock(const char *lxcpath, const char *name);
  82
  83 /*!
  84  * \brief Take an existing lock.
  85  *
  86  * \param lock Lock to operate on.
  87  * \param timeout Seconds to wait to take lock (\c 0 signifies an
  88  * indefinite wait).
  89  *
  90  * \return \c 0 if lock obtained, \c -2 on failure to set timeout,
  91  *  or \c -1 on any other error (\c errno will be set by \c sem_wait(3)
  92  * or \c fcntl(2)).
  93  *
  94  * \note \p timeout is (currently?) only supported for privlock, not
  95  * for slock.  Since currently there is not a single use of the timeout
  96  * (except in the test case) I may remove the support for it in sem as
  97  * well.
  98  */
  99 extern int lxclock(struct lxc_lock *lock, int timeout);
 100
 101 /*!
 102  * \brief Unlock specified lock previously locked using \ref lxclock().
 103  *
 104  * \param lock \ref lxc_lock.
 105  *
 106  * \return \c 0 on success, \c -2 if provided lock was not already held,
 107  * otherwise \c -1 with \c errno saved from \c fcntl(2) or sem_post function.
 108  */
 109 extern int lxcunlock(struct lxc_lock *lock);
 110
 111 /*!
 112  * \brief Free a lock created by \ref lxc_newlock().
 113  *
 114  * \param lock Lock.
 115  */
 116 extern void lxc_putlock(struct lxc_lock *lock);
 117
 118 /*!
 119  * \brief Lock the current process.
 120  */
 121 extern void process_lock(void);
 122
 123 /*!
 124  * \brief Unlock the current process.
 125  */
 126 extern void process_unlock(void);
 127
 128 struct lxc_container;
 129
 130 /*!
 131  * \brief Lock the containers memory.
 132  *
 133  * \param c Container.
 134  *
 135  * \return As for \ref lxclock().
 136  */
 137 extern int container_mem_lock(struct lxc_container *c);
 138
 139 /*!
 140  * \brief Unlock the containers memory.
 141  *
 142  * \param c Container.
 143  */
 144 extern void container_mem_unlock(struct lxc_container *c);
 145
 146 /*!
 147  * \brief Lock the containers disk data.
 148  *
 149  * \param c Container.
 150  *
 151  * \return \c 0 on success, or an \ref lxclock() error return
 152  * values on error.
 153  */
 154 extern int container_disk_lock(struct lxc_container *c);
 155
 156 /*!
 157  * \brief Unlock the containers disk data.
 158  *
 159  * \param c Container.
 160  *
 161  */
 162 extern void container_disk_unlock(struct lxc_container *c);
 163
 164 #endif