From: Linus Torvalds > Sent: 24 June 2023 00:32 > > On Fri, 23 Jun 2023 at 16:08, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > In fact, I'd expect that patch to fail immediately on a perfectly > > normal program that passes a token around by doing a small write to a > > pipe, and have the "token reader" do a bigger write. > > Bigger _read_, of course. > > This might be hidden by such programs typically doing a single byte > write and a single byte read, but I could easily imagine situations > where people actually depend on the POSIX atomicity guarantees, ie you > write a "token packet" that might be variable-sized, and the reader > then just does a maximally sized read, knowing that it will get a full > packet or nothing. There are definitely programs that just do a large read in order to consume all the single byte 'wakeup' writes. (The 'must check' on these reads is a right PITA.) They ought to set the pipe non-blocking, but I suspect many don't - because it all works anyway. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
