On Mon, Jan 20, 2025 at 11:24:56AM -0800, Linus Torvalds wrote: > On Sat, 18 Jan 2025 at 05:09, Christian Brauner <brauner@xxxxxxxxxx> wrote: > > > > Add a separate dio read align field to statx, as many out of place write > > file systems can easily do reads aligned to the device sector size, but > > require bigger alignment for writes. > > I've pulled this, but it needs some fixing. > > You added the 'dio_read_offset_align' field to 'struct kstat', and > that structure is *critical*, because it's used even for the real > 'stat()' calls that people actually use (as opposed to the statx side > that is seldom a real issue). > > And that field was added in a way that causes the struct to grow due > to alignment issues. For no good reason, because there were existing > holes in there. > > So please just fix it. Right, sorry I should've noticed that during review. > I despise the whole statx thing exactly because it has (approximately) > five specialized users, while slowing down regular stat/fstat that is > used widely absolutely *evertwhere*. > > Of course, judging by past performance, I wouldn't be surprised if > glibc has screwed the pooch, and decided to use 'statx()' to implement > stat, together with extra pointless user space overhead to convert one > into the other. Because that's the glibc way (ie the whole "turn > fstat() into the much slower fstatat() call, just because"). > > So here's the deal: 'statx()' is *not* an "improved stat". It's an > actively worse stat() for people who need very unusual and specialized > information, and it makes everything else worse. Yes, I'm well aware that you dislike statx(). :) It is heavily used nowadays though because there's a few additional bits in there that don't require calling into filesystems but are heavily used. I want to reiterate that if I'd been involved in statx() I would've done it as an extensible struct. So v1 of the struct would just be exactly what stat() was. This way neither copy-in nor copy-out would have done any unnecessary work and perf would've been the same. Only when userspace actually needed additional information it would have to pass in a larger struct and pay the price for copy-in and copy-out. I'll get you a new PR soon!
