On 2025/1/8 0:42, Christoph Hellwig wrote: > On Tue, Jan 07, 2025 at 10:05:47PM +0800, Zhang Yi wrote: >> Sorry. the "pure overwrites" and "always-cow files" makes me confused, >> this is mainly used to create a new written file range, but also could >> be used to zero out an existing range, why you mentioned it exists to >> facilitate pure overwrites? > > If you're fine with writes to your file causing block allocations you > can already use the hole punch or preallocate fallocate modes. No > need to actually send a command to the device. > Okay, I misunderstood your point earlier. This is indeed prepared for subsequent overwrites. Thanks a lot for explaining. Thanks, Yi. >> >> For the "always-cow files", do you mean reflinked files? Could you >> please give more details? > > reflinked files will require out of place writes for shared blocks. > As will anything on device mapper snapshots. Or any file on > file systems that write out of place (btrfs, f2fs, nilfs2, the > upcoming zoned xfs mode). >
