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/* This file handles advisory file locking as required by POSIX.
*
* The entry points into this file are
* lock_op: perform locking operations for FCNTL system call
* lock_revive: revive processes when a lock is released
*/
#include "fs.h"
#include <minix/com.h>
#include <minix/u64.h>
#include <fcntl.h>
#include <unistd.h>
#include <assert.h>
#include "file.h"
#include "lock.h"
#include "vnode.h"
/*===========================================================================*
* lock_op *
*===========================================================================*/
int lock_op(int fd, int req, vir_bytes arg)
{
/* Perform the advisory locking required by POSIX. */
int r, ltype, i, conflict = 0, unlocking = 0;
mode_t mo;
off_t first, last;
struct filp *f;
struct flock flock;
struct file_lock *flp, *flp2, *empty;
assert(req == F_GETLK || req == F_SETLK || req == F_SETLKW);
f = fp->fp_filp[fd];
assert(f != NULL);
/* Fetch the flock structure from user space. */
r = sys_datacopy_wrapper(who_e, arg, VFS_PROC_NR, (vir_bytes)&flock,
sizeof(flock));
if (r != OK) return(EINVAL);
/* Make some error checks. */
ltype = flock.l_type;
mo = f->filp_mode;
if (ltype != F_UNLCK && ltype != F_RDLCK && ltype != F_WRLCK) return(EINVAL);
if (req == F_GETLK && ltype == F_UNLCK) return(EINVAL);
if (!S_ISREG(f->filp_vno->v_mode) && !S_ISBLK(f->filp_vno->v_mode))
return(EINVAL);
if (req != F_GETLK && ltype == F_RDLCK && (mo & R_BIT) == 0) return(EBADF);
if (req != F_GETLK && ltype == F_WRLCK && (mo & W_BIT) == 0) return(EBADF);
/* Compute the first and last bytes in the lock region. */
switch (flock.l_whence) {
case SEEK_SET: first = 0; break;
case SEEK_CUR: first = f->filp_pos; break;
case SEEK_END: first = f->filp_vno->v_size; break;
default: return(EINVAL);
}
/* Check for overflow. */
if (((long) flock.l_start > 0) && ((first + flock.l_start) < first))
return(EINVAL);
if (((long) flock.l_start < 0) && ((first + flock.l_start) > first))
return(EINVAL);
first = first + flock.l_start;
last = first + flock.l_len - 1;
if (flock.l_len == 0) last = MAX_FILE_POS;
if (last < first) return(EINVAL);
/* Check if this region conflicts with any existing lock. */
empty = NULL;
for (flp = &file_lock[0]; flp < &file_lock[NR_LOCKS]; flp++) {
if (flp->lock_type == 0) {
if (empty == NULL) empty = flp;
continue; /* 0 means unused slot */
}
if (flp->lock_vnode != f->filp_vno) continue; /* different file */
if (last < flp->lock_first) continue; /* new one is in front */
if (first > flp->lock_last) continue; /* new one is afterwards */
if (ltype == F_RDLCK && flp->lock_type == F_RDLCK) continue;
if (ltype != F_UNLCK && flp->lock_pid == fp->fp_pid) continue;
/* There might be a conflict. Process it. */
conflict = 1;
if (req == F_GETLK) break;
/* If we are trying to set a lock, it just failed. */
if (ltype == F_RDLCK || ltype == F_WRLCK) {
if (req == F_SETLK) {
/* For F_SETLK, just report back failure. */
return(EAGAIN);
} else {
/* For F_SETLKW, suspend the process. */
fp->fp_flock.fd = fd;
fp->fp_flock.cmd = req;
fp->fp_flock.arg = arg;
suspend(FP_BLOCKED_ON_FLOCK);
return(SUSPEND);
}
}
/* We are clearing a lock and we found something that overlaps. */
unlocking = 1;
if (first <= flp->lock_first && last >= flp->lock_last) {
flp->lock_type = 0; /* mark slot as unused */
nr_locks--; /* number of locks is now 1 less */
continue;
}
/* Part of a locked region has been unlocked. */
if (first <= flp->lock_first) {
flp->lock_first = last + 1;
continue;
}
if (last >= flp->lock_last) {
flp->lock_last = first - 1;
continue;
}
/* Bad luck. A lock has been split in two by unlocking the middle. */
if (nr_locks == NR_LOCKS) return(ENOLCK);
for (i = 0; i < NR_LOCKS; i++)
if (file_lock[i].lock_type == 0) break;
flp2 = &file_lock[i];
flp2->lock_type = flp->lock_type;
flp2->lock_pid = flp->lock_pid;
flp2->lock_vnode = flp->lock_vnode;
flp2->lock_first = last + 1;
flp2->lock_last = flp->lock_last;
flp->lock_last = first - 1;
nr_locks++;
}
if (unlocking) lock_revive();
if (req == F_GETLK) {
if (conflict) {
/* GETLK and conflict. Report on the conflicting lock. */
flock.l_type = flp->lock_type;
flock.l_whence = SEEK_SET;
flock.l_start = flp->lock_first;
flock.l_len = flp->lock_last - flp->lock_first + 1;
flock.l_pid = flp->lock_pid;
} else {
/* It is GETLK and there is no conflict. */
flock.l_type = F_UNLCK;
}
/* Copy the flock structure back to the caller. */
r = sys_datacopy_wrapper(VFS_PROC_NR, (vir_bytes)&flock, who_e, arg,
sizeof(flock));
return(r);
}
if (ltype == F_UNLCK) return(OK); /* unlocked a region with no locks */
/* There is no conflict. If space exists, store new lock in the table. */
if (empty == NULL) return(ENOLCK); /* table full */
empty->lock_type = ltype;
empty->lock_pid = fp->fp_pid;
empty->lock_vnode = f->filp_vno;
empty->lock_first = first;
empty->lock_last = last;
nr_locks++;
return(OK);
}
/*===========================================================================*
* lock_revive *
*===========================================================================*/
void
lock_revive(void)
{
/* Go find all the processes that are waiting for any kind of lock and
* revive them all. The ones that are still blocked will block again when
* they run. The others will complete. This strategy is a space-time
* tradeoff. Figuring out exactly which ones to unblock now would take
* extra code, and the only thing it would win would be some performance in
* extremely rare circumstances (namely, that somebody actually used
* locking).
*/
struct fproc *fptr;
for (fptr = &fproc[0]; fptr < &fproc[NR_PROCS]; fptr++){
if (fptr->fp_pid == PID_FREE) continue;
if (fptr->fp_blocked_on == FP_BLOCKED_ON_FLOCK) {
revive(fptr->fp_endpoint, 0);
}
}
}
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