10:43 a.m.
On Tue, 2018-09-11 at 22:47 +0800, Kinglong Mee wrote:
On 2018/9/11 20:57, Trond Myklebust wrote:
> 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.
I think that's non-nfsv4.2's logical.
>
> 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.
>
No, if underlying filesystem is ext4/f2fs, or the nfs server is knfsd,
the last lseek syscall always return ENXIO no matter the cur_pos is > eof or
not.
A file ends with a hole as,
Part 22: DATA 0x0000000006a00000 ---> 0x0000000006afffff
Part 23: HOLE 0x0000000006b00000 ---> 0x000000000c7fffff
# stat testfile
File: testfile
Size: 209715200 Blocks: 22640 IO Block: 4096 regular file
Device: 807h/2055d Inode: 843122 Links: 2
Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2018-09-11 20:01:41.881227061 +0800
Modify: 2018-09-11 20:01:41.976478311 +0800
Change: 2018-09-11 20:01:41.976478311 +0800
Birth: -
# strace filemap testfile
... ...
lseek(3, 111149056, SEEK_HOLE) = 112197632
lseek(3, 112197632, SEEK_DATA) = -1 ENXIO (No such device or address)
Right now, when knfsd gets the ENXIO error, it returns the error to client
directly,
and return to syscall.
But, ganesha set the sr_eof to true and return NFS4_OK to client as RFC
description,
nfs client skips the sr_eof and return a bad offset to syscall.
Would it make more sense to change Knfsd instead of the client? I think I was
trying to keep things simple when I wrote the code, so I just passed the result
of the lseek system call back to the client.
Anna
thanks,
Kinglong Mee