On Wed, Jan 15, 2020 at 02:59:38PM +0000, David Howells wrote: > Another thread could be writing to the file at the same time, but not in the > same block. That's managed by netfs, most likely based on the pages and page > flags attached to the netfs inode being cached in this particular file[*]. > > What I was more thinking of is that SEEK_HOLE might run past the block of > interest and into a block that's currently being written and see a partially > written block. But that's not a problem given that you know where to search. > > [*] For AFS, this is only true of regular files; dirs and symlinks are cached > as monoliths and are there entirely or not at all. > > > > However, SEEK_HOLE doesn't help with the issue of the filesystem 'altering' > > > the content of the file by adding or removing blocks of zeros. > > > > As does any other method. If you need that fine grained control you > > need to track the information yourself. > > So, basically, I can't. Okay. I was hoping it might be possible to add an > ioctl or something to tell filesystems not to do that with particular files. File systems usually pad zeroes where they have to, typically for sub-blocksize writes. Disabling this would break data integrity.
