On Thu, Jan 27, 2022 at 09:03:36AM +1100, Daniel Black wrote: > On Wed, Jan 26, 2022 at 2:02 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Wed, Jan 26, 2022 at 09:05:48AM +1100, Daniel Black wrote: > > > > O_RDONLY is defined to be 0, so don't worry about it. > > Thanks. > > > > The kernel code in setfl seems to want to return EINVAL for > > > filesystems without a direct_IO structure member assigned, > > > > > > A noop_direct_IO seems to be used frequently to just return EINVAL > > > (like cifs_direct_io). > > > > Sorry for the confusion. You've caught us mid-transition. Eventually, > > ->direct_IO will be deleted, but for now it signifies whether or not the > > filesystem supports O_DIRECT, even though it's not used (except in some > > scenarios you don't care about). > > Is it going to be reasonable to expect fcntl(fd, F_SETFL, O_DIRECT) to > return EINVAL if O_DIRECT isn't supported? That is a reasonable expectation. I can't guarantee that we won't have bugs, of course ... > > > Lastly on the list of peculiar behaviors here, is tmpfs will return > > > EINVAL from the fcntl call however it works fine with O_DIRECT > > > (https://bugs.mysql.com/bug.php?id=26662). MySQL (and MariaDB still > > > has the same code) that currently ignores EINVAL, but I'm willing to > > > make that code better. > > > > Out of interest, what behaviour do you _want_ from doing O_DIRECT > > to tmpfs? O_DIRECT is defined to bypass the page cache, but tmpfs > > only stores data in the page cache. So what do you intend to happen? > > It occurs to me because EINVAL is returned, it's just operating in > non-O_DIRECT mode. > > It occurs to me that someone probably added this because (too much) > MySQL/MariaDB > testing is done on tmpfs and someone didn't want to adjust the test > suite to handle > failures everywhere on O_DIRECT. I don't think there was any kernel > expectation there. > > My problem it seems, I'll see what I can do to get back to using real > filesystems more. Heh. I know Hugh is looking at "supporting" O_DIRECT on tmpfs, at least for his internal testing. Not sure what his plans are for merging that support.
