Re: [PATCH 1/2] iohelper: skip lseek() and ftruncate() on block devices

Missed to answer part of your question. I'm using an NBD device backed by a userspace process using nbdkit, Simon ________________________________ From: Simon Rowe <simon.rowe(a)nutanix.com&gt; Sent: 23 August 2021 16:15 To: Michal Prívozník <mprivozn(a)redhat.com>; libvir-list(a)redhat.com <libvir-list(a)redhat.com&gt; Subject: Re: [PATCH 1/2] iohelper: skip lseek() and ftruncate() on block devices I'm using 5.4.109. I'll re-submit with changes to the second patch shortly, thanks Simon ________________________________ From: Michal Prívozník <mprivozn(a)redhat.com&gt; Sent: 23 August 2021 16:04 To: Simon Rowe <simon.rowe(a)nutanix.com>; libvir-list(a)redhat.com <libvir-list(a)redhat.com&gt; Subject: Re: [PATCH 1/2] iohelper: skip lseek() and ftruncate() on block devices On 8/23/21 4:38 PM, Simon Rowe wrote: Fair enough. I thought that block devices are always opened without poisoning host cache. If they aren't then you patch makes sense. But, what is your kernel version? Hopefully it's not too old. Is it a special block device or just some regular disk? Looking into the kernel code, it does implement O_DIRECT for block devices: kernel.git $ git grep -npC10 "\.direct_IO" -- fs/block_dev.c fs/block_dev.c-1680-} fs/block_dev.c-1681- fs/block_dev.c=1682=static const struct address_space_operations def_blk_aops = { fs/block_dev.c-1683- .set_page_dirty = __set_page_dirty_buffers, fs/block_dev.c-1684- .readpage = blkdev_readpage, fs/block_dev.c-1685- .readahead = blkdev_readahead, fs/block_dev.c-1686- .writepage = blkdev_writepage, fs/block_dev.c-1687- .write_begin = blkdev_write_begin, fs/block_dev.c-1688- .write_end = blkdev_write_end, fs/block_dev.c-1689- .writepages = blkdev_writepages, fs/block_dev.c:1690: .direct_IO = blkdev_direct_IO, fs/block_dev.c-1691- .migratepage = buffer_migrate_page_norefs, fs/block_dev.c-1692- .is_dirty_writeback = buffer_check_dirty_writeback, fs/block_dev.c-1693-}; fs/block_dev.c-1694- fs/block_dev.c-1695-#define BLKDEV_FALLOC_FL_SUPPORTED \ fs/block_dev.c-1696- (FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE | \ fs/block_dev.c-1697- FALLOC_FL_ZERO_RANGE | FALLOC_FL_NO_HIDE_STALE) fs/block_dev.c-1698- fs/block_dev.c-1699-static long blkdev_fallocate(struct file *file, int mode, loff_t start, fs/block_dev.c-1700- loff_t len) So it seems like your patch was correct after all. Would you like to resend this in v2 (I understand that patch 2/2 needs a rework) or do you want me to push this one right away? Michal