files/chiflag.c

This is files/chiflag.c, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it is the solution to Exercise 15-7 (page 309).

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

 

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  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* chiflag.c

   Change i-node flags (sometimes also known as ext2 extended file attributes)
   for files named on the command line. Usage is as shown in usageError() below.

   This program won't build on a system that takes its <linux/fs.h> from
   a kernel earlier than 2.6.19. You'll instead need to do something
   like including <linux/ext2_fs.h> and replacing all of the FS_* names
   below by EXT2_*.

   This program is Linux-specific.
*/
#define _GNU_SOURCE
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/fs.h>
#include "tlpi_hdr.h"
static void
usageError(const char *progName)
{
    fprintf(stderr, "Usage: %s {+-=}{attrib-chars} file...\n\n", progName);
#define fpe(str) fprintf(stderr, "    " str)            /* Shorter! */
    fpe("+ add attribute; - remove attribute; "
                        "= set attributes absolutely\n\n");
    fpe("'attrib-chars' contains one or more of:\n");
    fpe("    a   Force open() to include O_APPEND "
                        "(privilege required)\n");
    fpe("    A   Do not update last access time\n");
    fpe("    c   Compress (requires e2compr package)\n");
    fpe("    d   Do not backup with dump(8)\n");
    fpe("    D   Synchronous directory updates\n");
    fpe("    i   Immutable (privilege required)\n");
    fpe("    j   Enable ext3/ext4 data journaling\n");
    fpe("    s   Secure deletion (not implemented)\n");
    fpe("    S   Synchronous file updates\n");
    fpe("    t   Disable tail-packing (Reiserfs only)\n");
    fpe("    T   Mark as top-level directory for Orlov algorithm\n");
    fpe("    u   Undelete (not implemented)\n");
    exit(EXIT_FAILURE);
}
int
main(int argc, char *argv[])
{
    if (argc < 3 || strchr("+-=", argv[1][0]) == NULL ||
            strcmp(argv[1], "--help") == 0)
        usageError(argv[0]);

    /* Build bit mask based on attribute string in argv[1] */

    int attr = 0;
    for (char *p = &argv[1][1]; *p != '\0'; p++) {
        switch (*p) {
        case 'a': attr |= FS_APPEND_FL;         break;
        case 'A': attr |= FS_NOATIME_FL;        break;
        case 'c': attr |= FS_COMPR_FL;          break;
        case 'd': attr |= FS_NODUMP_FL;         break;
        case 'D': attr |= FS_DIRSYNC_FL;        break;
        case 'i': attr |= FS_IMMUTABLE_FL;      break;
        case 'j': attr |= FS_JOURNAL_DATA_FL;   break;
        case 's': attr |= FS_SECRM_FL;          break;
        case 'S': attr |= FS_SYNC_FL;           break;
        case 't': attr |= FS_NOTAIL_FL;         break;
        case 'T': attr |= FS_TOPDIR_FL;         break;
        case 'u': attr |= FS_UNRM_FL;           break;
        default:  usageError(argv[0]);
        }
    }

    /* Open each filename in turn, and change its attributes */

    for (int j = 2; j < argc; j++) {
        int fd = open(argv[j], O_RDONLY);
        if (fd == -1) {         /* Most likely error is nonexistent file */
            errMsg("open: %s", argv[j]);
            continue;
        }

        /* If argv[1] starts with + or -, then retrieve existing
           attribute bit mask and modify as required */

        if (argv[1][0] == '+' || argv[1][0] == '-') {
            int oldAttr;
            if (ioctl(fd, FS_IOC_GETFLAGS, &oldAttr) == -1)
                errExit("ioctl1: %s", argv[j]);
            attr = (*argv[1] == '-') ? (oldAttr & ~attr) : (oldAttr | attr);
        }

        if (ioctl(fd, FS_IOC_SETFLAGS, &attr) == -1)
            errExit("ioctl2: %s", argv[j]);
        if (close(fd) == -1)
            errExit("close");
    }

    exit(EXIT_SUCCESS);
}

 

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