How does this code from OS161 for finding a colon work?

Question

From here:

/*
 * Set bootfs_vnode.
 *
 * Bootfs_vnode is the vnode used for beginning path translation of
 * pathnames starting with /.
 *
 * It is also incidentally the system's first current directory.
 */
int
vfs_setbootfs(const char *fsname)
{
    char tmp[NAME_MAX+1];
    char *s;
    int result;
    struct vnode *newguy;

    vfs_biglock_acquire();

    snprintf(tmp, sizeof(tmp)-1, "%s", fsname);
    s = strchr(tmp, ':');
    if (s) {
        /* If there's a colon, it must be at the end */
        if (strlen(s)>0) {
            vfs_biglock_release();
            return EINVAL;
        }
    }
    else {
        strcat(tmp, ":");
    }

    result = vfs_chdir(tmp);
    if (result) {
        vfs_biglock_release();
        return result;
    }

    result = vfs_getcurdir(&newguy);
    if (result) {
        vfs_biglock_release();
        return result;
    }

    change_bootfs(newguy);

    vfs_biglock_release();
    return 0;
}

Why should strlen(s) be equal to zero? In other words, why if it's bigger than zero then return an error? Since the colon should be at the end if exists (as the comment says), shouldn't its size be 1?

The answer to 1 is the `snprintf`. The answer to 2 is a mystery. If `s` is not NULL after the `strchr`, then `strlen(s)` *must* be at least 1. — user3386109, Aug 29 '20 at 21:22
On your point (1): The `snprintf` function automatically appends the required `nul` terminating character to the target string, after the formatted output is performed. On point (2): I am as baffled as you. — Adrian Mole, Aug 29 '20 at 21:23
@user3386109 Hehe: 2 partial answers from two baffled observers. :) — Adrian Mole, Aug 29 '20 at 21:24
@AdrianMole Yup, either that's a bug, or a typo by the OP posting here. — user3386109, Aug 29 '20 at 21:25
I'm sure it's a bug never found, probably because it is not tested. — the busybee, Aug 31 '20 at 06:11

How does this code from OS161 for finding a colon work?

0 Answers0