On Fri 18-09-20 08:25:28, Mikulas Patocka wrote: > I'd like to ask about this problem: when we write to a file, the kernel > takes the write inode lock. When we read from a file, no lock is taken - > thus the read syscall can read data that are halfway modified by the write > syscall. > > The standard specifies the effects of the write syscall are atomic - see > this: > https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_09_07 Yes, but no Linux filesystem (except for XFS AFAIK) follows the POSIX spec in this regard. Mostly because the mixed read-write performance sucks when you follow it (not that it would absolutely have to suck - you can use clever locking with range locks but nobody does it currently). In practice, the read-write atomicity works on Linux only on per-page basis for buffered IO. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
