On Sat, Jul 04, 2020 at 09:12:06PM +0100, Al Viro wrote: > On Sat, Jul 04, 2020 at 09:41:09PM +0200, Miklos Szeredi wrote: > > And "If the size of file is smaller than the value provided in count > > then the whole file will be copied into buf", which is simply a lie; > > for example seq_file will happily return a smaller-than-PAGE_SIZE > > chunk if at least one record fits in there. You'll have a very hard > > time explaining that in the man page. So I think there are two > > possible ways forward: > > > > 1) just leave the first explanation (it's an open + read + close > > equivalent) and leave out the rest > > > > 2) add a loop around the vfs_read() in the code. > > 3) don't bother with the entire thing, until somebody manages to demonstrate > a setup where it does make a real difference (compared to than the obvious > sequence of syscalls, that is). At which point we'll need to figure out > what's going on and deal with the underlying problem of that setup. Incidentally, if that's intended for use on _sysfs_, I would like to see the effects of that sucker being called by many processes in parallel, seeing that sysfs has, er, certain scalability problems in its lookups. And I would be very surprised if they were not heavier than said overhead of two extra syscalls.
