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/*
* Copyright (c) 2017, NVIDIA CORPORATION. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
/*
* Four routines to be able to lock access to a file in the Linux
* approved manner. This seems to be the only method that works
* over NFS:
*
* __pg_make_lock_file( char* dir )
* Creates a uniquely-named file in the given directory.
* To work, this must be created on the same filesystem
* as the file which we are attempting to lock.
* If there are multiple processes running each competing for the
* same lock, each gets a unique file here.
* return -1 if it can't get a unique file in 50 tries
* __pg_get_lock( char* lname )
* The argument is the name of the lock.
* Each process tries to create a hard link with this name
* to its own uniquely-named file from __pg_make_lock_file().
* The one that succeeds is the new lock owner. The others
* fail and try again. There is a fail-over to handle the case
* where the process with the lock dies, which is inherently unsafe,
* but we haven't come up with a better solution.
* __pg_release_lock( char* lname )
* The argument is the same name for the lock.
* The lock is released by deleting (calling unlink) for the
* hard link we had just created.
* __pg_delete_lock_file()
* Clean up by deleting the uniquely named file we had created earlier.
*/
#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include "lockfile.h"
/*
* The name of the uniquely-named file and directory in which it is created
*/
static char *uname = NULL;
static char *udir = NULL;
/*
* Some counts for debugging
*/
static long uwaiting;
int
__pg_make_lock_file(char *dir)
{
pid_t pid;
char hostname[999];
int r;
FILE *F;
udir = (char *)malloc(strlen(dir) + 1);
strcpy(udir, dir);
pid = getpid();
r = gethostname(hostname, 998);
if (r != 0) {
fprintf(stderr, "gethostname fails\n");
exit(1);
}
uname = (char *)malloc(strlen(hostname) + strlen(udir) + 25);
r = 0;
do {
++r;
/* create a unique file */
sprintf(uname, "%s/lock.%s.%ld%d", udir, hostname, (long)pid, r);
F = fopen(uname, "w");
} while (F == NULL && r < 51);
if (F == NULL) {
return -1;
}
fprintf(F, "%s\n", uname);
fclose(F);
uwaiting = 0;
return 0;
} /* __pg_make_lock_file */
void
__pg_get_lock(char *lname)
{
int r;
struct stat ss, ss1;
int count;
char *fullname;
if (udir == NULL || uname == NULL)
return;
fullname = (char *)malloc(strlen(lname) + strlen(udir) +
2); /* +1 for / +1 for null terminator */
strcpy(fullname, udir);
strcat(fullname, "/");
strcat(fullname, lname);
memset(&ss1, 0, sizeof(ss1));
count = 0;
do {
r = link(uname, fullname);
if (r != 0) {
/* link had some problem, see if the number of links
* to the new file is now two */
r = stat(uname, &ss);
if (r == 0) {
if (ss.st_nlink != 2) {
if (ss.st_nlink != 1) {
fprintf(stderr, "get_lock: %d links to %s\n", (int)ss.st_nlink,
uname);
exit(1);
}
/* see if we should forcefully TAKE the lock */
r = lstat(fullname, &ss);
if (count == 0) {
memcpy(&ss1, &ss, sizeof(ss));
count = 1;
} else if (ss1.st_dev != ss.st_dev || ss1.st_ino != ss.st_ino ||
ss1.st_mode != ss.st_mode || ss1.st_uid != ss.st_uid ||
ss1.st_gid != ss.st_gid || ss1.st_size != ss.st_size ||
ss1.st_mtime != ss.st_mtime) {
/* some else got there first */
memcpy(&ss1, &ss, sizeof(ss));
count = 1;
} else {
++count;
if (count > 20) {
/* we've waited long enough. */
r = unlink(fullname);
/* ignore errors on the unlink */
}
}
sleep(1);
r = 1;
}
}
if (r)
++uwaiting;
}
} while (r != 0);
free(fullname);
} /* __pg_get_lock */
void
__pg_release_lock(char *lname)
{
int r;
char *fullname;
if (udir == NULL || uname == NULL)
return;
fullname = (char *)malloc(strlen(lname) + strlen(udir) + 2);
strcpy(fullname, udir);
strcat(fullname, "/");
strcat(fullname, lname);
/* release the lock by deleting the link */
r = unlink(fullname);
if (r != 0) {
fprintf(stderr, "release_lock: unlink %s fails\n", lname);
exit(1);
}
free(fullname);
} /* __pg_release_lock */
void
__pg_delete_lock_file()
{
int r;
/* delete the unique file */
r = unlink(uname);
if (r != 0) {
fprintf(stderr, "delete_lock_file: unlink %s fails\n", uname);
exit(1);
}
free(uname);
free(udir);
uname = NULL;
udir = NULL;
} /* __pg_delete_lock_file */
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