Supporting deeper symbolic links

Requiring the filesystem code and VFS code to be so intimately familiar with each other's use of stack space to avoid crashing the kernel is asking too much.

I too would expect an iteration to be the right fix. But if that's not practical, then the limit should be on the amount of stack space left, not the number of times a symbolic link has been followed. And it's actually cleaner to check how much stack space is left than to do the count. The code today doesn't do pure recursion; it has a special global (per-process) variable (current->link_count) it uses to determine when this particular recursion has hit its limit.

Think about /usr/bin/gcc where /usr is symlink to /mnt/somewhere/else and then ../bin/.. part is symlink as well and gcc too is symlink...

Now please about that tail recusion thingy again if you can. Heh.

Unfortunatelly you do care about path - just not path you though about...

As "track for stack usage" - it'll be nightmare to administer: sometimes you can compile this program but if b-tree in filesystem is changed somewhat you're suddenly can not do it. Gosh.

char real_name [path_max+1] = "";
char *s = link_name;
char *path_elem;
while ( path_elem = strstr(s, '/') ) {
    char r [path_max+1] = strcpy(real_name);
    int size;
    strcat(r, "/");
    strcat(r, path_elem);
    while ( (size = readlink(r, real_name)) != -1 ) {
        real_name[size] = NUL;
    }
    if ( size != EINVAL ) do_error_handling();
    s = NULL;
}