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:
- just leave the first explanation (it's an open + read + close
equivalent) and leave out the rest
- add a loop around the vfs_read() in the code.
- 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.