On Tue, Aug 12, 2025 at 05:08:18PM +0800, Chunsheng Luo wrote: > On 8/6/25 19:43, Bernd Schubert wrote: > > > On 8/6/25 11:17, Luis Henriques wrote: > >> On Tue, Aug 05 2025, Miklos Szeredi wrote: > >> > >>> The FUSE protocol uses struct fuse_write_out to convey the return value of > >>> copy_file_range, which is restricted to uint32_t. But the COPY_FILE_RANGE > >>> interface supports a 64-bit size copies. > >>> > >>> Currently the number of bytes copied is silently truncated to 32-bit, which > >>> is unfortunate at best. > >>> > >>> Introduce a new op COPY_FILE_RANGE_64, which is identical, except the > >>> number of bytes copied is returned in a 64-bit value. > >>> > >>> If the fuse server does not support COPY_FILE_RANGE_64, fall back to > >>> COPY_FILE_RANGE and truncate the size to UINT_MAX - 4096. > >> > >> I was wondering if it wouldn't make more sense to truncate the size to > >> MAX_RW_COUNT instead. My reasoning is that, if I understand the code > >> correctly (which is probably a big 'if'!), the VFS will fallback to > >> splice() if the file system does not implement copy_file_range. And in > >> this case splice() seems to limit the operation to MAX_RW_COUNT. > > > > I personally don't like the hard coded value too much and would use > > > > inarg.len = min_t(size_t, len, (UINT_MAX - 4096)); > > > > (btw, 0xfffff000 is UINT_MAX - 4095, isn't it?). > > > > Though that is all nitpick. The worst part that could happen are > > applications that do not handle partial file copy and then wouldn't > > copy the entire file. For these it probably would be better to return > > -ENOSYS. > > > > LGTM, > > > > Reviewed-by: Bernd Schubert <bschubert@xxxxxxx> > > Abot "truncate the size to UINT_MAX - 4096": > 4096 refers to PAGE_SIZE (the standard memory page size in most systems)? > If so, wouldn't UINT_MAX & PAGE_MASK be more appropriate? > like: `#define MAX_RW_COUNT (INT_MAX & PAGE_MASK)` > UINT_MAX & PAGE_MASK ensures the operation does not cross a page boundary. Yeah, I was wondering that too -- if we're going to cap a copy_file_range to something resembling MAX_RW_COUNT, then why not use that symbol directly? :) --D > Thanks > Chunsheng Luo >
