Messages in this thread | | | Date | Thu, 30 Mar 2006 10:10:09 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH][RFC] splice support |
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On Thu, Mar 30 2006, Andrew Morton wrote: > Jens Axboe <axboe@suse.de> wrote: > > > > > > ... > > > > > - I think the `size_t left' in do_splice_to() can overflow if f_pos is > > > sufficiently different from i_size. > > > > They're both loff_t. > > Nope: > > +static long do_splice_to(struct file *in, struct inode *pipe, size_t len, > + unsigned long flags) > +{ > + if (in->f_op && in->f_op->splice_read) { > + loff_t isize = i_size_read(in->f_mapping->host); > + size_t left; > + > + if (unlikely(in->f_pos >= isize)) > + return 0; > + > + left = isize - in->f_pos; > > It's doing > > 32bit = 64bit - 64bit;
My mistake, I looked at a different spot. Fixed.
> > > > > - In generic_file_splice_read(): > > > > > > - nonatomic modification of f_pos. Is i_mutex held? (see > > > generic_file_llseek()) > > > > Fixed. > > OK. In some ways I agree with Nick that a pwrite/pread-like interface is > nicer, so things are more stateless and threads don't have to fight over > f_pos. Dunno..
I can go either way, I tend to agree that passing in offset may be the best solution.
> > > - These pages can get truncated at any time they're unlocked. Does > > > the code cope with all that? > > > > I guess page_cache_pipe_buf_map() needs the same ->mapping check? > > That would seem appropriate. > > btw, that function might have a problem I think - it returns NULL with > the page locked, but pipe_to_sendpage() and other callers don't appear to > unlock it.
Will fix that up.
> > > - hm. What happens if the pages which find_get_pages() returned are > > > not contiguous in pagecache? I think your `pages' array gets all > > > jumbled up. > > > > Hmm please expand. > > find_get_pages() does "find me the next N pages above `index' which are > presently in pagecache'. So it can return an array of page*'s which do not > represent contiguous pages in the file - there can be holes in there. > > IOW: pages[n]->index !necessarily= pages[n+1]->index-1 > > Maybe the code handles that by making sure that all the pages in the range > are already in pagecache - I didn't check. But that would take some heroic > locking.
It doesn't, I'm assuming that find_get_pages() returns consequtive pages atm. Would seem like the sane interface :-)
We continue doing find_or_create_page() on the remaining, but using 'i' as the 'index' addition. So if we had non-conseq pages, we'd be screwed.
Needs a little thinking, input welcome..
-- Jens Axboe
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