On Tue, 2018-09-11 at 20:29 +0800, Kinglong Mee wrote: > The latest ganesha/gluster supports seek according to, > > https://tools.ietf.org/html/draft-ietf-nfsv4-minorversion2-41#section-15.11 > > From the given sa_offset, find the next data_content4 of type > sa_what > in the file. If the server can not find a corresponding sa_what, > then the status will still be NFS4_OK, but sr_eof would be > TRUE. If > the server can find the sa_what, then the sr_offset is the start > of > that content. If the sa_offset is beyond the end of the file, > then > SEEK MUST return NFS4ERR_NXIO. > > For a file's filemap as, > > Part 1: HOLE 0x0000000000000000 ---> 0x0000000000600000 > Part 2: DATA 0x0000000000600000 ---> 0x0000000000700000 > Part 3: HOLE 0x0000000000700000 ---> 0x0000000001000000 > > SEEK(0x700000, SEEK_DATA) gets result (sr_eof:1, sr_offset:0x70000) > from ganesha/gluster; > SEEK(0x700000, SEEK_HOLE) gets result (sr_eof:0, sr_offset:0x70000) > from ganesha/gluster. > > If an application depends the lseek result for data searching, it may > enter infinite loop. > > while (1) { > next_pos = lseek(fd, cur_pos, seek_type); > if (seek_type == SEEK_DATA) { > seek_type = SEEK_HOLE; > } else { > seek_type = SEEK_DATA; > } > > if (next_pos == -1) { > return ; > > cur_pos = next_pos; > } > > The lseek syscall always gets 0x70000 from nfs client for those two > cases, > but, if underlying filesystem is ext4/f2fs, or the nfs server is > knfsd, > the lseek(0x700000, SEEK_DATA) gets ENXIO. > > I wanna to know, > should I fix the ganesha/gluster as knfsd return ENXIO for the first > case? > or should I fix the nfs client to return ENXIO for the first case? > It that test correct? The fallback implementation of SEEK_DATA assumes that the entire file is data, so lseek(SEEK_DATA) on any offset that is <= eof will be a no-op. The fallback implementation of SEEK_HOLE assumes that the first hole is at eof. IOW: unless the initial value for cur_pos is > eof, it looks to me as if the above test will loop infinitely given any filesystem that doesn't implement native support for SEEK_DATA/SEEK_HOLE. -- Trond Myklebust Linux NFS client maintainer, Hammerspace trond.myklebust@xxxxxxxxxxxxxxx
