CODEWITHSUNDEEP
c
Neo
Neo

Reputation: 47

Permission in shmget() function in C

I have a quick question regarding shmget() function in C. The program is very simple. It asks user to enter a shmid, and it out puts Key, Mode, Owner etc.

I am using buffer->shm_perm.mode to get the permission but its giving the permissions in octal form (960 etc). Is there any way I can change it so it shows permission like "rwx"?

Thanks

Upvotes: 0

Views: 551

Answers (1)

Jonathan Leffler
Jonathan Leffler

Reputation: 754280

A (non-reentrant) function to convert a mode_t value into a string that might be produced by ls:

/*
** Convert a mode field into "ls -l" type perms field.
*/
static char *lsperms(int mode)
{
    static char *rwx[] = {"---", "--x", "-w-", "-wx",
    "r--", "r-x", "rw-", "rwx"};
    static char bits[11];

    bits[0] = filetypeletter(mode);
    strcpy(&bits[1], rwx[(mode >> 6) & 7]);
    strcpy(&bits[4], rwx[(mode >> 3) & 7]);
    strcpy(&bits[7], rwx[(mode & 7)]);
    if (mode & S_ISUID)
        bits[3] = (mode & 0100) ? 's' : 'S';
    if (mode & S_ISGID)
        bits[6] = (mode & 0010) ? 's' : 'l';
    if (mode & S_ISVTX)
        bits[9] = (mode & 0001) ? 't' : 'T';
    bits[10] = '\0';
    return(bits);
}

This can be simplified for shared memory since you don't need the file type (function not provided here anyway) or the special permissions bits.

/*
** Convert a mode field into "ls -l" type shared memory perms field.
*/
static char *shmperms(int mode)
{
    static char *rwx[] = {"---", "--x", "-w-", "-wx",
    "r--", "r-x", "rw-", "rwx"};
    static char bits[10];

    strcpy(&bits[0], rwx[(mode >> 6) & 7]);
    strcpy(&bits[3], rwx[(mode >> 3) & 7]);
    strcpy(&bits[6], rwx[(mode & 7)]);
    bits[9] = '\0';
    return(bits);
}

Upvotes: 2

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