minix/servers/vfs/lock.c

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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>
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#include <fcntl.h>
#include <unistd.h>
#include "file.h"
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#include "scratchpad.h"
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#include "lock.h"
#include "vnode.h"
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/*===========================================================================*
* lock_op *
*===========================================================================*/
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int lock_op(f, req)
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struct filp *f;
int req; /* either F_SETLK or F_SETLKW */
{
/* Perform the advisory locking required by POSIX. */
int r, ltype, i, conflict = 0, unlocking = 0;
mode_t mo;
off_t first, last;
struct flock flock;
struct file_lock *flp, *flp2, *empty;
/* Fetch the flock structure from user space. */
r = sys_datacopy(who_e, (vir_bytes) scratch(fp).io.io_buffer, VFS_PROC_NR,
(vir_bytes) &flock, sizeof(flock));
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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);
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if (!S_ISREG(f->filp_vno->v_mode) && !S_ISBLK(f->filp_vno->v_mode))
return(EINVAL);
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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) {
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case SEEK_SET: first = 0; break;
case SEEK_CUR: first = f->filp_pos; break;
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case SEEK_END: first = f->filp_vno->v_size; break;
default: return(EINVAL);
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}
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/* Check for overflow. */
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if (((long) flock.l_start > 0) && ((first + flock.l_start) < first))
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return(EINVAL);
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if (((long) flock.l_start < 0) && ((first + flock.l_start) > first))
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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++) {
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if (flp->lock_type == 0) {
if (empty == NULL) empty = flp;
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continue; /* 0 means unused slot */
}
if (flp->lock_vnode != f->filp_vno) continue; /* different file */
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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;
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/* 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. */
suspend(FP_BLOCKED_ON_LOCK);
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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;
}
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/* 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;
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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(VFS_PROC_NR, (vir_bytes) &flock, who_e,
(vir_bytes) scratch(fp).io.io_buffer, sizeof(flock));
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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 */
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empty->lock_type = ltype;
empty->lock_pid = fp->fp_pid;
empty->lock_vnode = f->filp_vno;
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empty->lock_first = first;
empty->lock_last = last;
nr_locks++;
return(OK);
}
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/*===========================================================================*
* lock_revive *
*===========================================================================*/
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void lock_revive()
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{
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/* 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
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* locking).
*/
struct fproc *fptr;
for (fptr = &fproc[0]; fptr < &fproc[NR_PROCS]; fptr++){
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if (fptr->fp_pid == PID_FREE) continue;
if (fptr->fp_blocked_on == FP_BLOCKED_ON_LOCK) {
endpoint-aware conversion of servers. 'who', indicating caller number in pm and fs and some other servers, has been removed in favour of 'who_e' (endpoint) and 'who_p' (proc nr.). In both PM and FS, isokendpt() convert endpoints to process slot numbers, returning OK if it was a valid and consistent endpoint number. okendpt() does the same but panic()s if it doesn't succeed. (In PM, this is pm_isok..) pm and fs keep their own records of process endpoints in their proc tables, which are needed to make kernel calls about those processes. message field names have changed. fs drivers are endpoints. fs now doesn't try to get out of driver deadlock, as the protocol isn't supposed to let that happen any more. (A warning is printed if ELOCKED is detected though.) fproc[].fp_task (indicating which driver the process is suspended on) became an int. PM and FS now get endpoint numbers of initial boot processes from the kernel. These happen to be the same as the old proc numbers, to let user processes reach them with the old numbers, but FS and PM don't know that. All new processes after INIT, even after the generation number wraps around, get endpoint numbers with generation 1 and higher, so the first instances of the boot processes are the only processes ever to have endpoint numbers in the old proc number range. More return code checks of sys_* functions have been added. IS has become endpoint-aware. Ditched the 'text' and 'data' fields in the kernel dump (which show locations, not sizes, so aren't terribly useful) in favour of the endpoint number. Proc number is still visible. Some other dumps (e.g. dmap, rs) show endpoint numbers now too which got the formatting changed. PM reading segments using rw_seg() has changed - it uses other fields in the message now instead of encoding the segment and process number and fd in the fd field. For that it uses _read_pm() and _write_pm() which to _taskcall()s directly in pm/misc.c. PM now sys_exit()s itself on panic(), instead of sys_abort(). RS also talks in endpoints instead of process numbers.
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revive(fptr->fp_endpoint, 0);
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}
}
}