On Fri, Jul 03, 2020 at 11:53:24AM +0200, Andreas Gruenbacher wrote: > Add an IOCB_NOIO flag that indicates to generic_file_read_iter that it > shouldn't trigger any filesystem I/O for the actual request or for > readahead. This allows to do tentative reads out of the page cache as > some filesystems allow, and to take the appropriate locks and retry the > reads only if the requested pages are not cached. > > Signed-off-by: Andreas Gruenbacher <agruenba@xxxxxxxxxx> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > @@ -2249,9 +2253,18 @@ EXPORT_SYMBOL_GPL(generic_file_buffered_read); > * > * This is the "read_iter()" routine for all filesystems > * that can use the page cache directly. > + * > + * The IOCB_NOWAIT flag in iocb->ki_flags indicates that -EAGAIN shall > + * be returned when no data can be read without waiting for I/O requests > + * to complete; it doesn't prevent readahead. > + * > + * The IOCB_NOIO flag in iocb->ki_flags indicates that -EAGAIN shall be > + * returned when no data can be read without issuing new I/O requests, > + * and 0 shall be returned when readhead would have been triggered. s/shall/may/ -- if we read a previous page then hit a readahead page, we'll return a positive value. If the first page we hit is a readahead page, then yes, we'll return zero. Again, I'm happy for the patch to go in as-is without this nitpick.
