+/* i_fcntl_locking.c
+
+ Usage: i_fcntl_locking file...
+
+ where 'file...' is a list of files on which to place locks - the user is
+ then prompted to interactively enter commands to test/place locks on
+ regions of the files.
+
+ NOTE: The version of the program provided here is an enhanced version
+ of that provided in the book. In particular, this version:
+
+ 1) handles multiple file name arguments, allowing locks to be
+ applied to any of the named files,
+ 2) displays information about whether advisory or mandatory
+ locking is in effect on each file, and
+ 3) allows the use of OFD locks, a type of file lock added in
+ Linux 3.15.
+*/
+#define _GNU_SOURCE /* To get definitions of 'OFD' locking commands */
#include <sys/stat.h>
#include <fcntl.h>
#include "tlpi_hdr.h"
#define MAX_LINE 100
+#ifdef __linux__
+#ifndef F_OFD_GETLK /* In case we are on a system with glibc version
+ earlier than 2.20 */
+#define F_OFD_GETLK 36
+#define F_OFD_SETLK 37
+#define F_OFD_SETLKW 38
+#endif
+#endif
+
+/* Return TRUE if mandatory locking is enabled for fd. */
+
+static Boolean
+mandLockingEnabled(int fd)
+{
+ /* Mandatory locking is enabled for a file if the set-group-ID bit is on
+ but group-execute permission is off (a combination that under earlier
+ versions of UNIX had no useful meaning). If mandatory locking is enabled
+ for a file, then attempts to perform write(2) or read(2) calls on locked
+ regions of files will block until the lock is removed (or if the I/O
+ call is nonblocking it will return immediately with an error). */
+
+ struct stat sb;
+
+ if (fstat(fd, &sb) == -1)
+ errExit("stat");
+ return (sb.st_mode & S_ISGID) != 0 && (sb.st_mode & S_IXGRP) == 0;
+}
+
static void
-displayCmdFmt(void)
+displayCmdFmt(int argc, char *argv[], const int fdList[])
{
- printf("\n Format: cmd lock start length [whence]\n\n");
+ int j;
+
+ if (argc == 2) { /* Only a single filename argument */
+ printf("\nFormat: cmd lock start length [whence]\n\n");
+ } else {
+ printf("\nFormat: %scmd lock start length [whence]\n\n",
+ (argc > 2) ? "file-num " : "");
+ printf(" file-num is a number from the following list\n");
+ for (j = 1; j < argc; j++)
+ printf(" %2d %-10s [%s locking]\n", j, argv[j],
+ mandLockingEnabled(fdList[j]) ? "mandatory" : "advisory");
+ }
printf(" 'cmd' is 'g' (GETLK), 's' (SETLK), or 'w' (SETLKW)\n");
+#ifdef __linux__
+ printf(" or for OFD locks: 'G' (OFD_GETLK), 'S' (OFD_SETLK), or "
+ "'W' (OFD_SETLKW)\n");
+#endif
printf(" 'lock' is 'r' (READ), 'w' (WRITE), or 'u' (UNLOCK)\n");
printf(" 'start' and 'length' specify byte range to lock\n");
printf(" 'whence' is 's' (SEEK_SET, default), 'c' (SEEK_CUR), "
"or 'e' (SEEK_END)\n\n");
+ /* Of course, SEEK_CUR is redundant since we can't
+ change the file offset in this program... */
}
int
main(int argc, char *argv[])
{
int fd, numRead, cmd, status;
char lock, cmdCh, whence, line[MAX_LINE];
struct flock fl;
long long len, st;
+ int *fdList;
+ int fileNum, j;
- if (argc != 2 || strcmp(argv[1], "--help") == 0)
- usageErr("%s file\n", argv[0]);
+ if (argc < 2 || strcmp(argv[1], "--help") == 0)
+ usageErr("%s file...\n", argv[0]);
- fd = open(argv[1], O_RDWR);
- if (fd == -1)
- errExit("open (%s)", argv[1]);
+ fdList = calloc(argc, sizeof(int));
+ if (fdList == NULL)
+ errExit("calloc");
+
+ for (j = 1; j < argc; j++) {
+ fdList[j] = open(argv[j], O_RDWR);
+ if (fdList[j] == -1)
+ errExit("open (%s)", argv[j]);
+ }
+
+ /* Inform user what type of locking is in effect for each file. */
+
+ printf("File Locking\n");
+ printf("---- -------\n");
+
+ for (j = 1; j < argc; j++)
+ printf("%-10s %s\n", argv[j], mandLockingEnabled(fdList[j]) ?
+ "mandatory" : "advisory");
+ printf("\n");
printf("Enter ? for help\n");
for (;;) { /* Prompt for locking command and carry it out */
printf("PID=%ld> ", (long) getpid());
fflush(stdout);
if (fgets(line, MAX_LINE, stdin) == NULL) /* EOF */
exit(EXIT_SUCCESS);
line[strlen(line) - 1] = '\0'; /* Remove trailing '\n' */
if (*line == '\0')
continue; /* Skip blank lines */
if (line[0] == '?') {
- displayCmdFmt();
+ displayCmdFmt(argc, argv, fdList);
continue;
}
whence = 's'; /* In case not otherwise filled in */
- numRead = sscanf(line, "%c %c %lld %lld %c", &cmdCh, &lock,
- &st, &len, &whence);
+ if (argc == 2) { /* Just 1 file arg on command line? */
+ fileNum = 1; /* Then no need to read a file number */
+ numRead = sscanf(line, " %c %c %lld %lld %c",
+ &cmdCh, &lock, &st, &len, &whence);
+ } else {
+ numRead = sscanf(line, "%d %c %c %lld %lld %c",
+ &fileNum, &cmdCh, &lock, &st, &len, &whence);
+ }
+
fl.l_start = st;
fl.l_len = len;
- if (numRead < 4 || strchr("gsw", cmdCh) == NULL ||
+ if (fileNum < 1 || fileNum >= argc) {
+ printf("File number must be in range 1 to %d\n", argc-1);
+ continue;
+ }
+
+ fd = fdList[fileNum];
+
+ if (!((numRead >= 4 && argc == 2) || (numRead >= 5 && argc > 2)) ||
+ strchr("gswGSW", cmdCh) == NULL ||
strchr("rwu", lock) == NULL || strchr("sce", whence) == NULL) {
printf("Invalid command!\n");
continue;
}
- cmd = (cmdCh == 'g') ? F_GETLK : (cmdCh == 's') ? F_SETLK : F_SETLKW;
+ cmd =
+#ifdef __linux__
+ (cmdCh == 'G') ? F_OFD_GETLK : (cmdCh == 'S') ? F_OFD_SETLK :
+ (cmdCh == 'W') ? F_OFD_SETLKW :
+#endif
+ (cmdCh == 'g') ? F_GETLK : (cmdCh == 's') ? F_SETLK : F_SETLKW;
+#ifdef __linux__
+ fl.l_pid = 0; /* Required for 'OFD' locking commands */
+#endif
fl.l_type = (lock == 'r') ? F_RDLCK : (lock == 'w') ? F_WRLCK : F_UNLCK;
fl.l_whence = (whence == 'c') ? SEEK_CUR :
(whence == 'e') ? SEEK_END : SEEK_SET;
status = fcntl(fd, cmd, &fl); /* Perform request... */
- if (cmd == F_GETLK) { /* ... and see what happened */
+ if (cmd == F_GETLK
+#ifdef __linux__
+ || cmd == F_OFD_GETLK
+#endif
+ ) {
if (status == -1) {
- errMsg("fcntl - F_GETLK");
+ errMsg("fcntl");
} else {
if (fl.l_type == F_UNLCK)
printf("[PID=%ld] Lock can be placed\n", (long) getpid());
else /* Locked out by someone else */
printf("[PID=%ld] Denied by %s lock on %lld:%lld "
"(held by PID %ld)\n", (long) getpid(),
(fl.l_type == F_RDLCK) ? "READ" : "WRITE",
(long long) fl.l_start,
(long long) fl.l_len, (long) fl.l_pid);
}
- } else { /* F_SETLK, F_SETLKW */
+ } else {
if (status == 0)
printf("[PID=%ld] %s\n", (long) getpid(),
(lock == 'u') ? "unlocked" : "got lock");
- else if (errno == EAGAIN || errno == EACCES) /* F_SETLK */
+ else if (errno == EAGAIN || errno == EACCES)
printf("[PID=%ld] failed (incompatible lock)\n",
(long) getpid());
else if (errno == EDEADLK) /* F_SETLKW */
printf("[PID=%ld] failed (deadlock)\n", (long) getpid());
else
- errMsg("fcntl - F_SETLK(W)");
+ errMsg("fcntl");
}
}
}
