On Mon, Mar 30, 2015 at 3:36 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> 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? > >> 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. I'm okay with an old or nothing flag. Although I think that would much more useful with RWF_NONWAIT with pwritev, in applications that don't want to block while logging (but it's okay to drop low level log messages). That's a whole different use case in my mind. -- Milosz Tanski CTO 16 East 34th Street, 15th floor New York, NY 10016 p: 646-253-9055 e: milosz@xxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
