> On Jan 20, 2018, at 8:07 PM, Jens Axboe <axboe@xxxxxxxxx> wrote: > > On 1/20/18 7:23 PM, Goldwyn Rodrigues wrote: >> >> >> On 01/20/2018 08:11 PM, Andi Kleen wrote: >>> >>> It's likely there's a lot of code in user space that does >>> >>> if (write(..., N) < 0) handle error >>> >>> With your change it would need to be >>> >>> if (write(..., N) != N) handle error >>> >>> How much code is actually doing that? >>> >>> I can understand it fixes your artifical test suite, but it seems to me your >>> change has a high potential to break a lot of existing user code >>> in subtle ways. So it seems to be a bad idea. >> >> >> Quoting 'man 2 write': >> >> RETURN VALUE >> On success, the number of bytes written is returned (zero indicates >> nothing was written). It is not an error if this number is smaller >> than the number of bytes requested; this may happen for example because >> the disk device was filled. See also NOTES. > > You can quote as much man page as you want - Andi is well aware of how > read/write system call works, as I'm sure all of us are, that is not the > issue. The issue is that there are potentially LOTS of applications out > there that do not check for short writes, they do exactly what Andi > speculated above. If you break it with this change, it doesn't matter > what's in the man page. What matters is previous behavior, and that > you are breaking user space. At that point nobody cares what's in the > man page. Applications that don't handle partial writes are already broken with buffered I/O, this change doesn't really make them more broken. Cheers, Andreas
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