Re: [patch] s_maxbytes handling

[Andrew Morton <andrewm@uow.edu.au>]

Alan Cox wrote:
> 
> > If ->f_pos is positioned exactly at sb->s_maxbytes, a non-zero-length
> > write to the file doesn't write anything, and write() returns zero.
> 
> Are you absolutely sure here. Because I ran that code through a set of standards
> verification tests. So unless you can cite page and paragraph from SuS and
> the LFS spec I think the 0 might in fact be correct..

I don't know the standards Alan, but returning zero
from write() when f_pos is at s_maxbytes will make
a lot of apps hang up.  dd, bash and zsh certainly do.

Are they buggy?  Should they be testing the return value
of write() and assuming that zero is file-full?

The s_maxbytes logic is different from the
MAX_NON_LFS logic:

        /*
         *      LFS rule 
         */
        if ( pos + count > MAX_NON_LFS && !(file->f_flags&O_LARGEFILE)) {
                if (pos >= MAX_NON_LFS) {
                        send_sig(SIGXFSZ, current, 0);
                        goto out;
                }

This makes more sense.  If the file is full, and
you're trying to grow it, you fail.