/*
* linux/fs/locks.c
*
* Provide support for fcntl()'s F_GETLK, F_SETLK, and F_SETLKW calls.
* Doug Evans (dje@spiff.uucp), August 07, 1992
*
* Deadlock detection added.
* FIXME: one thing isn't handled yet:
* - mandatory locks (requires lots of changes elsewhere)
* Kelly Carmichael (kelly@[142.24.8.65]), September 17, 1994.
*
* Miscellaneous edits, and a total rewrite of posix_lock_file() code.
* Kai Petzke (wpp@marie.physik.tu-berlin.de), 1994
*
* Converted file_lock_table to a linked list from an array, which eliminates
* the limits on how many active file locks are open.
* Chad Page (pageone@netcom.com), November 27, 1994
*
* Removed dependency on file descriptors. dup()'ed file descriptors now
* get the same locks as the original file descriptors, and a close() on
* any file descriptor removes ALL the locks on the file for the current
* process. Since locks still depend on the process id, locks are inherited
* after an exec() but not after a fork(). This agrees with POSIX, and both
* BSD and SVR4 practice.
* Andy Walker (andy@lysaker.kvaerner.no), February 14, 1995
*
* Scrapped free list which is redundant now that we allocate locks
* dynamically with kmalloc()/kfree().
* Andy Walker (andy@lysaker.kvaerner.no), February 21, 1995
*
* Implemented two lock personalities - FL_FLOCK and FL_POSIX.
*
* FL_POSIX locks are created with calls to fcntl() and lockf() through the
* fcntl() system call. They have the semantics described above.
*
* FL_FLOCK locks are created with calls to flock(), through the flock()
* system call, which is new. Old C libraries implement flock() via fcntl()
* and will continue to use the old, broken implementation.
*
* FL_FLOCK locks follow the 4.4 BSD flock() semantics. They are associated
* with a file pointer (filp). As a result they can be shared by a parent
* process and its children after a fork(). They are removed when the last
* file descriptor referring to the file pointer is closed (unless explicitly
* unlocked).
*
* FL_FLOCK locks never deadlock, an existing lock is always removed before
* upgrading from shared to exclusive (or vice versa). When this happens
* any processes blocked by the current lock are woken up and allowed to
* run before the new lock is applied.
* Andy Walker (andy@lysaker.kvaerner.no), June 09, 1995
*
* Removed some race conditions in flock_lock_file(), marked other possible
* races. Just grep for FIXME to see them.
* Dmitry Gorodchanin (begemot@bgm.rosprint.net), February 09, 1996.
*
* Addressed Dmitry's concerns. Deadlock checking no longer recursive.
* Lock allocation changed to GFP_ATOMIC as we can't afford to sleep
* once we've checked for blocking and deadlocking.
* Andy Walker (andy@lysaker.kvaerner.no), April 03, 1996.
*
* Initial implementation of mandatory locks. SunOS turned out to be
* a rotten model, so I implemented the "obvious" semantics.
* See 'linux/Documentation/mandatory.txt' for details.
* Andy Walker (andy@lysaker.kvaerner.no), April 06, 1996.
*
* Don't allow mandatory locks on mmap()'ed files. Added simple functions to
* check if a file has mandatory locks, used by mmap(), open() and creat() to
* see if system call should be rejected. Ref. HP-UX/SunOS/Solaris Reference
* Manual, Section 2.
* Andy Walker (andy@lysaker.kvaerner.no), April 09, 1996.
*
* Tidied up block list handling. Added '/proc/locks' interface.
* Andy Walker (andy@lysaker.kvaerner.no), April 24, 1996.
*
* Fixed deadlock condition for pathological code that mixes calls to
* flock() and fcntl().
* Andy Walker (andy@lysaker.kvaerner.no), April 29, 1996.
*
* Allow only one type of locking scheme (FL_POSIX or FL_FLOCK) to be in use
* for a given file at a time. Changed the CONFIG_LOCK_MANDATORY scheme to
* guarantee sensible behaviour in the case where file system modules might
* be compiled with different options than the kernel itself.
* Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
*
* Added a couple of missing wake_up() calls. Thanks to Thomas Meckel
* (Thomas.Meckel@mni.fh-giessen.de) for spotting this.
* Andy Walker (andy@lysaker.kvaerner.no), May 15, 1996.
*
* Changed FL_POSIX locks to use the block list in the same way as FL_FLOCK
* locks. Changed process synchronisation to avoid dereferencing locks that
* have already been freed.
* Andy Walker (andy@lysaker.kvaerner.no), Sep 21, 1996.
*
* Made the block list a circular list to minimise searching in the list.
* Andy Walker (andy@lysaker.kvaerner.no), Sep 25, 1996.
*
* Made mandatory locking a mount option. Default is not to allow mandatory
* locking.
* Andy Walker (andy@lysaker.kvaerner.no), Oct 04, 1996.
*
* Fixed /proc/locks interface so that we can't overrun the buffer we are handed.
* Andy Walker (andy@lysaker.kvaerner.no), May 12, 1997.
*/
#include <linux/malloc.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/stat.h>
#include <linux/fcntl.h>
#include <asm/segment.h>
#define OFFSET_MAX ((off_t)0x7fffffff) /* FIXME: move elsewhere? */
static int flock_make_lock(struct file *filp, struct file_lock *fl,
unsigned int cmd);
static int posix_make_lock(struct file *filp, struct file_lock *fl,
struct flock *l);
static int flock_locks_conflict(struct file_lock *caller_fl,
struct file_lock *sys_fl);
static int posix_locks_conflict(struct file_lock *caller_fl,
struct file_lock *sys_fl);
static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl);
static int flock_lock_file(struct file *filp, struct file_lock *caller,
unsigned int wait);
static int posix_lock_file(struct file *filp, struct file_lock *caller,
unsigned int wait);
static int posix_locks_deadlock(struct task_struct *my_task,
struct task_struct *blocked_task);
static void posix_remove_locks(struct file_lock **before, struct task_struct *task);
static void flock_remove_locks(struct file_lock **before, struct file *filp);
static struct file_lock *locks_empty_lock(void);
static struct file_lock *locks_init_lock(struct file_lock *,
struct file_lock *);
static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl);
static void locks_delete_lock(struct file_lock **thisfl_p, unsigned int wait);
static char *lock_get_status(struct file_lock *fl, int id, char *pfx);
static void locks_insert_block(struct file_lock *blocker, struct file_lock *waiter);
static void locks_delete_block(struct file_lock *blocker, struct file_lock *waiter);
static void locks_wake_up_blocks(struct file_lock *blocker, unsigned int wait);
static struct file_lock *file_lock_table = NULL;
/* Allocate a new lock, and initialize its fields from fl.
* The lock is not inserted into any lists until locks_insert_lock() or
* locks_insert_block() are called.
*/
static inline struct file_lock *locks_alloc_lock(struct file_lock *fl)
{
return locks_init_lock(locks_empty_lock(), fl);
}
/* Free lock not inserted in any queue.
*/
static inline void locks_free_lock(struct file_lock *fl)
{
if (waitqueue_active(&fl->fl_wait))
panic("Aarggh: attempting to free lock with active wait queue - shoot Andy");
if (fl->fl_nextblock != NULL || fl->fl_prevblock != NULL)
panic("Aarggh: attempting to free lock with active block list - shoot Andy");
kfree(fl);
return;
}
/* Check if two locks overlap each other.
*/
static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
{
return ((fl1->fl_end >= fl2->fl_start) &&
(fl2->fl_end >= fl1->fl_start));
}
/* Insert waiter into blocker's block list.
* We use a circular list so that processes can be easily woken up in
* the order they blocked. The documentation doesn't require this but
* it seems seems like the reasonable thing to do.
*/
static void locks_insert_block(struct file_lock *blocker,
struct file_lock *waiter)
{
struct file_lock *prevblock;
if (blocker->fl_prevblock == NULL)
/* No previous waiters - list is empty */
prevblock = blocker;
else
/* Previous waiters exist - add to end of list */
prevblock = blocker->fl_prevblock;
prevblock->fl_nextblock = waiter;
blocker->fl_prevblock = waiter;
waiter->fl_nextblock = blocker;
waiter->fl_prevblock = prevblock;
return;
}
/* Remove waiter from blocker's block list.
* When blocker ends up pointing to itself then the list is empty.
*/
static void locks_delete_block(struct file_lock *blocker,
struct file_lock *waiter)
{
struct file_lock *nextblock;
struct file_lock *prevblock;
nextblock = waiter->fl_nextblock;
prevblock = waiter->fl_prevblock;
if (nextblock == NULL)
return;
nextblock->fl_prevblock = prevblock;
prevblock->fl_nextblock = nextblock;
waiter->fl_prevblock = waiter->fl_nextblock = NULL;
if (blocker->fl_nextblock == blocker)
/* No more locks on blocker's blocked list */
blocker->fl_prevblock = blocker->fl_nextblock = NULL;
return;
}
/* Wake up processes blocked waiting for blocker.
* If told to wait then schedule the processes until the block list
* is empty, otherwise empty the block list ourselves.
*/
static void locks_wake_up_blocks(struct file_lock *blocker, unsigned int wait)
{
struct file_lock *waiter;
while ((waiter = blocker->fl_nextblock) != NULL) {
wake_up(&waiter->fl_wait);
if (wait)
/* Let the blocked process remove waiter from the
* block list when it gets scheduled.
*/
schedule();
else
/* Remove waiter from the block list, because by the
* time it wakes up blocker won't exist any more.
*/
locks_delete_block(blocker, waiter);
}
return;
}
/* flock() system call entry point. Apply a FL_FLOCK style lock to
* an open file descriptor.
*/
asmlinkage int sys_flock(unsigned int fd, unsigned int cmd)
{
struct file_lock file_lock;
struct file *filp;
if ((fd >= NR_OPEN) || !(filp = current->files->fd[fd]))
return (-EBADF);
if (!flock_make_lock(filp, &file_lock, cmd))
return (-EINVAL);
if ((file_lock.fl_type != F_UNLCK) && !(filp->f_mode & 3))
return (-EBADF);
return (flock_lock_file(filp, &file_lock, (cmd & (LOCK_UN | LOCK_NB)) ? 0 : 1));
}
/* Report the first existing lock that would conflict with l.
* This implements the F_GETLK command of fcntl().
*/
int fcntl_getlk(unsigned int fd, struct flock *l)
{
int error;
struct flock flock;
struct file *filp;
struct file_lock *fl,file_lock;
if ((fd >= NR_OPEN) || !(filp = current->files->fd[fd]))
return (-EBADF);
error = verify_area(VERIFY_WRITE, l, sizeof(*l));
if (error)
return (error);
memcpy_fromfs(&flock, l, sizeof(flock));
if ((flock.l_type != F_RDLCK) && (flock.l_type != F_WRLCK))
return (-EINVAL);
if (!filp->f_inode || !posix_make_lock(filp, &file_lock, &flock))
return (-EINVAL);
flock.l_type = F_UNLCK;
for (fl = filp->f_inode->i_flock; fl != NULL; fl = fl->fl_next) {
if (!(fl->fl_flags & FL_POSIX))
break;
if (posix_locks_conflict(&file_lock, fl)) {
flock.l_pid = fl->fl_owner->pid;
flock.l_start = fl->fl_start;
flock.l_len = fl->fl_end == OFFSET_MAX ? 0 :
fl->fl_end - fl->fl_start + 1;
flock.l_whence = 0;
flock.l_type = fl->fl_type;
break;
}
}
memcpy_tofs(l, &flock, sizeof(flock));
return (0);
}
/* Apply the lock described by l to an open file descriptor.
* This implements both the F_SETLK and F_SETLKW commands of fcntl().
* It also emulates flock() in a pretty broken way for older C
* libraries.
*/
int fcntl_setlk(unsigned int fd, unsigned int cmd, struct flock *l)
{
int error;
struct file *filp;
struct file_lock file_lock;
struct flock flock;
struct inode *inode;
/* Get arguments and validate them ...
*/
if ((fd >= NR_OPEN) || !(filp = current->files->fd[fd]))
return (-EBADF);
error = verify_area(VERIFY_READ, l, sizeof(*l));
if (error)
return (error);
if (!(inode = filp->f_inode))
return (-EINVAL);
/*
* This might block, so we do it before checking the inode.
*/
memcpy_fromfs(&flock, l, sizeof(flock));
/* Don't allow mandatory locks on files that may be memory mapped
* and shared.
*/
if (IS_MANDLOCK(inode) &&
(inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID &&
inode->i_mmap) {
struct vm_area_struct *vma = inode->i_mmap;
do {
if (vma->vm_flags & VM_MAYSHARE)
return (-EAGAIN);
vma = vma->vm_next_share;
} while (vma != inode->i_mmap);
}
if (!posix_make_lock(filp, &file_lock, &flock))
return (-EINVAL);
switch (flock.l_type) {
case F_RDLCK:
if (!(filp->f_mode & 1))
return (-EBADF);
break;
case F_WRLCK:
if (!(filp->f_mode & 2))
return (-EBADF);
break;
case F_UNLCK:
break;
case F_SHLCK:
case F_EXLCK:
#if 1
/* warn a bit for now, but don't overdo it */
{
static int count = 0;
if (!count) {
count=1;
printk(KERN_WARNING
"fcntl_setlk() called by process %d (%s) with broken flock() emulation\n",
current->pid, current->comm);
}
}
#endif
if (!(filp->f_mode & 3))
return (-EBADF);
break;
default:
return (-EINVAL);
}
return (posix_lock_file(filp, &file_lock, cmd == F_SETLKW));
}
/* This function is called when the file is closed.
*/
void locks_remove_locks(struct task_struct *task, struct file *filp)
{
struct file_lock *fl;
/* For POSIX locks we free all locks on this file for the given task.
* For FLOCK we only free locks on this *open* file if it is the last
* close on that file.
*/
if ((fl = filp->f_inode->i_flock) != NULL) {
if (fl->fl_flags & FL_POSIX)
posix_remove_locks(&filp->f_inode->i_flock, task);
else
flock_remove_locks(&filp->f_inode->i_flock, filp);
}
return;
}
static void posix_remove_locks(struct file_lock **before, struct task_struct *task)
{
struct file_lock *fl;
while ((fl = *before) != NULL) {
if (fl->fl_owner == task)
locks_delete_lock(before, 0);
else
before = &fl->fl_next;
}
return;
}
static void flock_remove_locks(struct file_lock **before, struct file *filp)
{
struct file_lock *fl;
while ((fl = *before) != NULL) {
if ((fl->fl_file == filp) && (filp->f_count == 1))
locks_delete_lock(before, 0);
else
before = &fl->fl_next;
}
return;
}
int locks_verify_locked(struct inode *inode)
{
/* Candidates for mandatory locking have the setgid bit set
* but no group execute bit - an otherwise meaningless combination.
*/
if (IS_MANDLOCK(inode) &&
(inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
return (locks_mandatory_locked(inode));
return (0);
}
int locks_verify_area(int read_write, struct inode *inode, struct file *filp,
unsigned int offset, unsigned int count)
{
/* Candidates for mandatory locking have the setgid bit set
* but no group execute bit - an otherwise meaningless combination.
*/
if (IS_MANDLOCK(inode) &&
(inode->i_mode & (S_ISGID | S_IXGRP)) == S_ISGID)
return (locks_mandatory_area(read_write, inode, filp, offset,
count));
return (0);
}
int locks_mandatory_locked(struct inode *inode)
{
struct file_lock *fl;
/* If there are no FL_POSIX locks then go ahead. */
if (!(fl = inode->i_flock) || !(fl->fl_flags & FL_POSIX))
return (0);
/* Search the lock list for this inode for any POSIX locks.
*/
while (fl != NULL) {
if (fl->fl_owner != current)
return (-EAGAIN);
fl = fl->fl_next;
}
return (0);
}
int locks_mandatory_area(int read_write, struct inode *inode,
struct file *filp, unsigned int offset,
unsigned int count)
{
struct file_lock *fl;
struct file_lock tfl;
memset(&tfl, 0, sizeof(tfl));
tfl.fl_file = filp;
tfl.fl_flags = FL_POSIX | FL_ACCESS;
tfl.fl_owner = current;
tfl.fl_type = (read_write == FLOCK_VERIFY_WRITE) ? F_WRLCK : F_RDLCK;
tfl.fl_start = offset;
tfl.fl_end = offset + count - 1;
repeat:
/* If there are no FL_POSIX locks then go ahead. */
if (!(fl = inode->i_flock) || !(fl->fl_flags & FL_POSIX))
return (0);
/* Search the lock list for this inode for locks that conflict with
* the proposed read/write.
*/
while (fl != NULL) {
/* Block for writes against a "read" lock,
* and both reads and writes against a "write" lock.
*/
if (posix_locks_conflict(fl, &tfl)) {
if (filp && (filp->f_flags & O_NONBLOCK))
return (-EAGAIN);
if (current->signal & ~current->blocked)
return (-ERESTARTSYS);
if (posix_locks_deadlock(current, fl->fl_owner))
return (-EDEADLK);
locks_insert_block(fl, &tfl);
interruptible_sleep_on(&tfl.fl_wait);
locks_delete_block(fl, &tfl);
if (current->signal & ~current->blocked)
return (-ERESTARTSYS);
/* If we've been sleeping someone might have
* changed the permissions behind our back.
*/
if ((inode->i_mode & (S_ISGID | S_IXGRP)) != S_ISGID)
break;
goto repeat;
}
fl = fl->fl_next;
}
return (0);
}
/* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
* style lock.
*/
static int posix_make_lock(struct file *filp, struct file_lock *fl,
struct flock *l)
{
off_t start;
memset(fl, 0, sizeof(*fl));
fl->fl_flags = FL_POSIX;
switch (l->l_type) {
case F_RDLCK:
case F_WRLCK:
case F_UNLCK:
fl->fl_type = l->l_type;
break;
case F_SHLCK :
fl->fl_type = F_RDLCK;
fl->fl_flags |= FL_BROKEN;
break;
case F_EXLCK :
fl->fl_type = F_WRLCK;
fl->fl_flags |= FL_BROKEN;
break;
default:
return (0);
}
switch (l->l_whence) {
case 0: /*SEEK_SET*/
start = 0;
break;
case 1: /*SEEK_CUR*/
start = filp->f_pos;
break;
case 2: /*SEEK_END*/
start = filp->f_inode->i_size;
break;
default:
return (0);
}
if (((start += l->l_start) < 0) || (l->l_len < 0))
return (0);
fl->fl_start = start; /* we record the absolute position */
if ((l->l_len == 0) || ((fl->fl_end = start + l->l_len - 1) < 0))
fl->fl_end = OFFSET_MAX;
fl->fl_file = filp;
fl->fl_owner = current;
return (1);
}
/* Verify a call to flock() and fill in a file_lock structure with
* an appropriate FLOCK lock.
*/
static int flock_make_lock(struct file *filp, struct file_lock *fl,
unsigned int cmd)
{
memset(fl, 0, sizeof(*fl));
if (!filp->f_inode) /* just in case */
return (0);
switch (cmd & ~LOCK_NB) {
case LOCK_SH:
fl->fl_type = F_RDLCK;
break;
case LOCK_EX:
fl->fl_type = F_WRLCK;
break;
case LOCK_UN:
fl->fl_type = F_UNLCK;
break;
default:
return (0);
}
fl->fl_flags = FL_FLOCK;
fl->fl_start = 0;
fl->fl_end = OFFSET_MAX;
fl->fl_file = filp;
fl->fl_owner = NULL;
return (1);
}
/* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
* checking before calling the locks_conflict().
*/
static int posix_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
/* POSIX locks owned by the same process do not conflict with
* each other.
*/
if (caller_fl->fl_owner == sys_fl->fl_owner)
return (0);
return (locks_conflict(caller_fl, sys_fl));
}
/* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
* checking before calling the locks_conflict().
*/
static int flock_locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
/* FLOCK locks referring to the same filp do not conflict with
* each other.
*/
if (caller_fl->fl_file == sys_fl->fl_file)
return (0);
return (locks_conflict(caller_fl, sys_fl));
}
/* Determine if lock sys_fl blocks lock caller_fl. Common functionality
* checks for overlapping locks and shared/exclusive status.
*/
static int locks_conflict(struct file_lock *caller_fl, struct file_lock *sys_fl)
{
if (!locks_overlap(caller_fl, sys_fl))
return (0);
switch (caller_fl->fl_type) {
case F_RDLCK:
return (sys_fl->fl_type == F_WRLCK);
case F_WRLCK:
return (1);
default:
printk("locks_conflict(): impossible lock type - %d\n",
caller_fl->fl_type);
break;
}
return (0); /* This should never happen */
}
/* This function tests for deadlock condition before putting a process to
* sleep. The detection scheme is no longer recursive. Recursive was neat,
* but dangerous - we risked stack corruption if the lock data was bad, or
* if the recursion was too deep for any other reason.
*
* We rely on the fact that a task can only be on one lock's wait queue
* at a time. When we find blocked_task on a wait queue we can re-search
* with blocked_task equal to that queue's owner, until either blocked_task
* isn't found, or blocked_task is found on a queue owned by my_task.
*/
static int posix_locks_deadlock(struct task_struct *my_task,
struct task_struct *blocked_task)
{
struct file_lock *fl;
struct file_lock *bfl;
next_task:
if (my_task == blocked_task)
return (1);
for (fl = file_lock_table; fl != NULL; fl = fl->fl_nextlink) {
if (fl->fl_owner == NULL || fl->fl_nextblock == NULL)
continue;
for (bfl = fl->fl_nextblock; bfl != fl; bfl = bfl->fl_nextblock) {
if (bfl->fl_owner == blocked_task) {
if (fl->fl_owner == my_task) {
return (1);
}
blocked_task = fl->fl_owner;
goto next_task;
}
}
}
return (0);
}
/* Try to create a FLOCK lock on filp. We always insert new FLOCK locks at
* the head of the list, but that's secret knowledge known only to the next
* two functions.
*/
static int flock_lock_file(struct file *filp, struct file_lock *caller,
unsigned int wait)
{
struct file_lock *fl;
struct file_lock *new_fl = NULL;
struct file_lock **before;
int error;
int change;
int unlock = (caller->fl_type == F_UNLCK);
/*
* If we need a new lock, get it in advance to avoid races.
*/
if (!unlock) {
error = -ENOLCK;
new_fl = locks_alloc_lock(caller);
if (!new_fl)
goto out;
}
error = 0;
search:
change = 0;
before = &filp->f_inode->i_flock;
if ((fl = *before) && (fl->fl_flags & FL_POSIX)) {
error = -EBUSY;
goto out;
}
while ((fl = *before) != NULL) {
if (caller->fl_file == fl->fl_file) {
if (caller->fl_type == fl->fl_type)
goto out;
change = 1;
break;
}
before = &fl->fl_next;
}
/* change means that we are changing the type of an existing lock, or
* or else unlocking it.
*/
if (change) {
/* N.B. What if the wait argument is false? */
locks_delete_lock(before, !unlock);
/*
* If we waited, another lock may have been added ...
*/
if (!unlock)
goto search;
}
if (unlock)
goto out;
repeat:
/* Check signals each time we start */
error = -ERESTARTSYS;
if (current->signal & ~current->blocked)
goto out;
error = -EBUSY;
if ((fl = filp->f_inode->i_flock) && (fl->fl_flags & FL_POSIX))
goto out;
while (fl != NULL) {
if (!flock_locks_conflict(new_fl, fl)) {
fl = fl->fl_next;
continue;
}
error = -EAGAIN;
if (!wait)
goto out;
locks_insert_block(fl, new_fl);
interruptible_sleep_on(&new_fl->fl_wait);
locks_delete_block(fl, new_fl);
goto repeat;
}
locks_insert_lock(&filp->f_inode->i_flock, new_fl);
new_fl = NULL;
error = 0;
out:
if (new_fl)
locks_free_lock(new_fl);
return (error);
}
/* Add a POSIX style lock to a file.
* We merge adjacent locks whenever possible. POSIX locks are sorted by owner
* task, then by starting address
*
* Kai Petzke writes:
* To make freeing a lock much faster, we keep a pointer to the lock before the
* actual one. But the real gain of the new coding was, that lock_it() and
* unlock_it() became one function.
*
* To all purists: Yes, I use a few goto's. Just pass on to the next function.
*/
static int posix_lock_file(struct file *filp, struct file_lock *caller,
unsigned int wait)
{
struct file_lock *fl;
struct file_lock *new_fl, *new_fl2;
struct file_lock *left = NULL;
struct file_lock *right = NULL;
struct file_lock **before;
int error;
int added = 0;
/*
* We may need two file_lock structures for this operation,
* so we get them in advance to avoid races.
*/
new_fl = locks_empty_lock();
new_fl2 = locks_empty_lock();
error = -ENOLCK; /* "no luck" */
if (!(new_fl && new_fl2))
goto out;
if (caller->fl_type != F_UNLCK) {
repeat:
error = -EBUSY;
if ((fl = filp->f_inode->i_flock) && (fl->fl_flags & FL_FLOCK))
goto out;
while (fl != NULL) {
if (!posix_locks_conflict(caller, fl)) {
fl = fl->fl_next;
continue;
}
error = -EAGAIN;
if (!wait)
goto out;
error = -EDEADLK;
if (posix_locks_deadlock(caller->fl_owner, fl->fl_owner))
goto out;
error = -ERESTARTSYS;
if (current->signal & ~current->blocked)
goto out;
locks_insert_block(fl, caller);
interruptible_sleep_on(&caller->fl_wait);
locks_delete_block(fl, caller);
goto repeat;
}
}
/*
* We've allocated the new locks in advance, so there are no
* errors possible (and no blocking operations) from here on.
*
* Find the first old lock with the same owner as the new lock.
*/
before = &filp->f_inode->i_flock;
error = -EBUSY;
if ((*before != NULL) && ((*before)->fl_flags & FL_FLOCK))
goto out;
/* First skip locks owned by other processes.
*/
while ((fl = *before) && (caller->fl_owner != fl->fl_owner)) {
before = &fl->fl_next;
}
/* Process locks with this owner.
*/
while ((fl = *before) && (caller->fl_owner == fl->fl_owner)) {
/* Detect adjacent or overlapping regions (if same lock type)
*/
if (caller->fl_type == fl->fl_type) {
if (fl->fl_end < caller->fl_start - 1)
goto next_lock;
/* If the next lock in the list has entirely bigger
* addresses than the new one, insert the lock here.
*/
if (fl->fl_start > caller->fl_end + 1)
break;
/* If we come here, the new and old lock are of the
* same type and adjacent or overlapping. Make one
* lock yielding from the lower start address of both
* locks to the higher end address.
*/
if (fl->fl_start > caller->fl_start)
fl->fl_start = caller->fl_start;
else
caller->fl_start = fl->fl_start;
if (fl->fl_end < caller->fl_end)
fl->fl_end = caller->fl_end;
else
caller->fl_end = fl->fl_end;
if (added) {
locks_delete_lock(before, 0);
continue;
}
caller = fl;
added = 1;
}
else {
/* Processing for different lock types is a bit
* more complex.
*/
if (fl->fl_end < caller->fl_start)
goto next_lock;
if (fl->fl_start > caller->fl_end)
break;
if (caller->fl_type == F_UNLCK)
added = 1;
if (fl->fl_start < caller->fl_start)
left = fl;
/* If the next lock in the list has a higher end
* address than the new one, insert the new one here.
*/
if (fl->fl_end > caller->fl_end) {
right = fl;
break;
}
if (fl->fl_start >= caller->fl_start) {
/* The new lock completely replaces an old
* one (This may happen several times).
*/
if (added) {
locks_delete_lock(before, 0);
continue;
}
/* Replace the old lock with the new one.
* Wake up anybody waiting for the old one,
* as the change in lock type might satisfy
* their needs.
*/
locks_wake_up_blocks(fl, 0);
fl->fl_start = caller->fl_start;
fl->fl_end = caller->fl_end;
fl->fl_type = caller->fl_type;
caller = fl;
added = 1;
}
}
/* Go on to next lock.
*/
next_lock:
before = &fl->fl_next;
}
error = 0;
if (!added) {
if (caller->fl_type == F_UNLCK)
goto out;
locks_init_lock(new_fl, caller);
locks_insert_lock(before, new_fl);
new_fl = NULL;
}
if (right) {
if (left == right) {
/* The new lock breaks the old one in two pieces,
* so we have to use the second new lock (in this
* case, even F_UNLCK may fail!).
*/
left = locks_init_lock(new_fl2, right);
locks_insert_lock(before, left);
new_fl2 = NULL;
}
right->fl_start = caller->fl_end + 1;
locks_wake_up_blocks(right, 0);
}
if (left) {
left->fl_end = caller->fl_start - 1;
locks_wake_up_blocks(left, 0);
}
out:
/*
* Free any unused locks. (They haven't
* ever been used, so we use kfree().)
*/
if (new_fl)
kfree(new_fl);
if (new_fl2)
kfree(new_fl2);
return error;
}
/*
* Allocate an empty lock structure. We can use GFP_KERNEL now that
* all allocations are done in advance.
*/
static struct file_lock *locks_empty_lock(void)
{
return ((struct file_lock *) kmalloc(sizeof(struct file_lock),
GFP_KERNEL));
}
/*
* Initialize a new lock from an existing file_lock structure.
*/
static struct file_lock *locks_init_lock(struct file_lock *new,
struct file_lock *fl)
{
if (new) {
memset(new, 0, sizeof(*new));
new->fl_owner = fl->fl_owner;
new->fl_file = fl->fl_file;
new->fl_flags = fl->fl_flags;
new->fl_type = fl->fl_type;
new->fl_start = fl->fl_start;
new->fl_end = fl->fl_end;
}
return new;
}
/* Insert file lock fl into an inode's lock list at the position indicated
* by pos. At the same time add the lock to the global file lock list.
*/
static void locks_insert_lock(struct file_lock **pos, struct file_lock *fl)
{
fl->fl_nextlink = file_lock_table;
fl->fl_prevlink = NULL;
if (file_lock_table != NULL)
file_lock_table->fl_prevlink = fl;
file_lock_table = fl;
fl->fl_next = *pos; /* insert into file's list */
*pos = fl;
return;
}
/* Delete a lock and free it.
* First remove our lock from the active lock lists. Then call
* locks_wake_up_blocks() to wake up processes that are blocked
* waiting for this lock. Finally free the lock structure.
*/
static void locks_delete_lock(struct file_lock **thisfl_p, unsigned int wait)
{
struct file_lock *thisfl;
struct file_lock *prevfl;
struct file_lock *nextfl;
thisfl = *thisfl_p;
*thisfl_p = thisfl->fl_next;
prevfl = thisfl->fl_prevlink;
nextfl = thisfl->fl_nextlink;
if (nextfl != NULL)
nextfl->fl_prevlink = prevfl;
if (prevfl != NULL)
prevfl->fl_nextlink = nextfl;
else
file_lock_table = nextfl;
locks_wake_up_blocks(thisfl, wait);
locks_free_lock(thisfl);
return;
}
static char *lock_get_status(struct file_lock *fl, int id, char *pfx)
{
static char temp[129];
char *p = temp;
struct inode *inode;
inode = fl->fl_file->f_inode;
p += sprintf(p, "%d:%s ", id, pfx);
if (fl->fl_flags & FL_POSIX) {
p += sprintf(p, "%6s %s ",
(fl->fl_flags & FL_BROKEN) ? "BROKEN" :
(fl->fl_flags & FL_ACCESS) ? "ACCESS" : "POSIX ",
(IS_MANDLOCK(inode) &&
(inode->i_mode & (S_IXGRP | S_ISGID)) == S_ISGID) ?
"MANDATORY" : "ADVISORY ");
}
else {
p += sprintf(p, "FLOCK ADVISORY ");
}
p += sprintf(p, "%s ", (fl->fl_type == F_RDLCK) ? "READ " : "WRITE");
p += sprintf(p, "%d %s:%ld %ld %ld ",
fl->fl_owner ? fl->fl_owner->pid : 0,
kdevname(inode->i_dev), inode->i_ino, fl->fl_start,
fl->fl_end);
sprintf(p, "%08lx %08lx %08lx %08lx %08lx\n",
(long)fl, (long)fl->fl_prevlink, (long)fl->fl_nextlink,
(long)fl->fl_next, (long)fl->fl_nextblock);
return (temp);
}
static inline int copy_lock_status(char *p, char **q, off_t pos, int len,
off_t offset, int length)
{
int i;
i = pos - offset;
if (i > 0) {
if (i >= length) {
i = len + length - i;
memcpy(*q, p, i);
*q += i;
return (0);
}
if (i < len) {
p += len - i;
}
else
i = len;
memcpy(*q, p, i);
*q += i;
}
return (1);
}
int get_locks_status(char *buffer, char **start, off_t offset, int length)
{
struct file_lock *fl;
struct file_lock *bfl;
char *p;
char *q = buffer;
int i;
int len;
off_t pos = 0;
for (fl = file_lock_table, i = 1; fl != NULL; fl = fl->fl_nextlink, i++) {
p = lock_get_status(fl, i, "");
len = strlen(p);
pos += len;
if (!copy_lock_status(p, &q, pos, len, offset, length))
goto done;
if ((bfl = fl->fl_nextblock) == NULL)
continue;
do {
p = lock_get_status(bfl, i, " ->");
len = strlen(p);
pos += len;
if (!copy_lock_status(p, &q, pos, len, offset, length))
goto done;
} while ((bfl = bfl->fl_nextblock) != fl);
}
done:
if (q != buffer)
*start = buffer;
return (q - buffer);
}
