From: Lennert Buytenhek > Sent: 28 January 2021 23:07 > > On Sun, Jan 24, 2021 at 10:21:38PM +0000, David Laight wrote: > > > > One open question is whether IORING_OP_GETDENTS64 should be more like > > > pread(2) and allow passing in a starting offset to read from the > > > directory from. (This would require some more surgery in fs/readdir.c.) > > > > Since directories are seekable this ought to work. > > Modulo horrid issues with 32bit file offsets. > > The incremental patch below does this. (It doesn't apply cleanly on > top of v1 of the IORING_OP_GETDENTS patch as I have other changes in > my tree -- I'm including it just to illustrate the changes that would > make this work.) > > This change seems to work, and makes IORING_OP_GETDENTS take an > explicitly specified directory offset (instead of using the file's > ->f_pos), making it more like pread(2), and I like the change from > a conceptual point of view, but it's a bit ugly around > iterate_dir_use_ctx_pos(). Any thoughts on how to do this more > cleanly (without breaking iterate_dir() semantics)? I had a further thought... I presume the basic operation is: lock(file); do_getents(); // Updates file->offset unlock(file); Which means you can implement an offset by saving, updating and restoring file->offset while the lock is held. This is a bit like the completely broken pread() in uclibc which uses two lseek() calls to set and restore the offset. Whoever wrote that needs shooting - worse than useless. Glibc is as bad: // Don't even ask what glibc's clock_nanosleep() does, you don't want to know. while (syscall(SYS_clock_nanosleep, CLOCK_MONOTONIC, TIMER_ABSTIME, &ts, NULL) David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
