On Mon, Mar 30, 2015 at 12:36:04AM -0700, Christoph Hellwig wrote: > On Fri, Mar 27, 2015 at 08:58:54AM -0700, Jeremy Allison wrote: > > The problem with the above is that we can't tell the difference > > between pread2() returning a short read because the pages are not > > in cache, or because someone truncated the file. So we need some > > way to differentiate this. > > Is a race vs truncate really that time critical that you can't > wait for the thread pool to do the second read to notice it? Probably not, as this is the fallback path anyway. > > My preference from userspace would be for pread2() to return > > EAGAIN if *all* the data requested is not available (where > > 'all' can be less than the size requested if the file has > > been truncated in the meantime). > > That is easily implementable, but I can see that for example web apps > would be happy to get as much as possible. So if Samba can be ok > with short reads and only detecting the truncated case in the slow > path that would make life simpler. Otherwise we might indeed need two > flags. Simpler is better. I can live with the partial read+fallback. Jeremy. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
