7:57 a.m.
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(a)hammerspace.com