glusterfs

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#include <stdio.h>
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#include <fcntl.h>
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#include <errno.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/wait.h>
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#define LOG_ERR(func, err)                                                     \
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    do {                                                                       \
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        fprintf(stderr, "%s : returned error (%s)\n", func, strerror(err));    \
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        exit(err);                                                             \
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    } while (0)
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int fd;
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struct flock lock;
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char *buf = "ten bytes!";
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char *fname = "/mnt/glusterfs/0/mand.lock";
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int open_flags, child, err, status, blocked = 0;
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int
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do_child(char *argv[])
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{
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    /* Initialize file open flags */
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    if (strcmp(argv[2], "BLOCK") == 0)
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        open_flags = O_RDWR;
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    else if (strcmp(argv[2], "TRUNC") == 0)
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        open_flags = O_RDWR | O_TRUNC | O_NONBLOCK;
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    else if (strcmp(argv[2], "NONE") == 0)
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        open_flags = O_RDWR | O_NONBLOCK;
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    else
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        LOG_ERR("Invalid option:", EINVAL);
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    /* Open the file */
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    fd = open(fname, open_flags);
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    if (fd == -1)
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        LOG_ERR("Child open", errno);
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    /* Perform the file operation*/
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    if (strcmp(argv[3], "READ") == 0) {
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        buf = NULL;
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        err = read(fd, buf, 10);
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        if (err == -1)
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            LOG_ERR("Child read", errno);
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    } else if (strcmp(argv[3], "WRITE") == 0) {
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        err = write(fd, buf, 10);
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        if (err == -1)
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            LOG_ERR("Child write", errno);
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    } else if (strcmp(argv[3], "FTRUNCATE") == 0) {
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        err = ftruncate(fd, 5);
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        if (err)
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            LOG_ERR("Child ftruncate", errno);
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    } else
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        LOG_ERR("Invalid operation:", EINVAL);
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    /* Close child fd */
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    err = close(fd);
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    if (err)
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        LOG_ERR("Child close", errno);
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    /* Exit success */
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    exit(0);
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}
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int
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main(int argc, char *argv[])
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{
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    if (argc < 4) {
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        fprintf(stderr,
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                "Wrong usage: Use as ./mandatory-lock "
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                "<RD_LCK/WR_LCK> <BLOCK/TRUNC/NONE> "
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                "<READ/WRITE/FTRUNCATE\n");
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        exit(EINVAL);
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    }
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    /* Create an empty lock file */
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    fd = open(fname, O_CREAT | O_RDWR, 0755);
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    if (fd == -1)
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        LOG_ERR("Parent create", errno);
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    /* Determine the type of lock */
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    if (strcmp(argv[1], "RD_LCK") == 0)
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        lock.l_type = F_RDLCK;
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    else if (strcmp(argv[1], "WR_LCK") == 0)
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        lock.l_type = F_WRLCK;
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    else
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        LOG_ERR("Parent lock type", EINVAL);
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    lock.l_whence = SEEK_SET;
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    lock.l_start = 0L;
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    lock.l_len = 0L;
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    /* Let parent acquire the initial lock */
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    err = fcntl(fd, F_SETLK, &lock);
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    if (err)
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        LOG_ERR("Parent lock", errno);
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    /* Now fork a child */
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    child = fork();
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    if (child == 0)
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        /* Perform the child operations */
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        do_child(argv);
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    else {
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        /* If blocking mode, then sleep for 2 seconds
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         * and wait for the child */
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        if (strcmp(argv[2], "NONE") != 0) {
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            sleep(2);
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            if (waitpid(child, &status, WNOHANG) == 0)
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                blocked = 1;
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            /* Release the parent lock so that the
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             * child can terminate */
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            lock.l_type = F_UNLCK;
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            err = fcntl(fd, F_SETLK, &lock);
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            if (err)
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                LOG_ERR("Parent unlock", errno);
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        }
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        /* Wait for child to finish */
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        waitpid(child, &status, 0);
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        /* Close the parent fd */
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        err = close(fd);
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        if (err)
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            LOG_ERR("Parent close", errno);
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        /* Remove the lock file*/
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        err = unlink(fname);
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        if (err)
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            LOG_ERR("Parent unlink", errno);
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        /* If not blocked, exit with child exit status*/
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        errno = WEXITSTATUS(status);
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        /* If blocked, exit with corresponding
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         * error code */
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        if (blocked)
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            errno = EWOULDBLOCK;
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        if (errno != 0)
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            printf("%s\n", strerror(errno));
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        exit(errno);
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    }
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}
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