Question on continuous EIOs in CIFS protocol
Volker.Lendecke at SerNet.DE
Thu Sep 18 12:49:11 MDT 2014
From this snipped I can't really tell what your big picture
looks like. Can you please post the whole thing somewhere?
I'd be happy with your patchset, as long as I can cleanly
apply this to 3.5.15.
On Thu, Sep 18, 2014 at 11:28:34AM -0700, sandeep nag wrote:
> We are using 3.5.15 + Async IO + few patches.
> Here is the code:
> In the write() call path we call ' cifs_wd_to_buf()'
> static cifs_error_t
> wdata_t *wd,
> char *buf,
> size_t n)
> size_t bytes_read = 0;
> size_t num_continuous_interupts = 0;
> ssize_t read_ret = -1;
> cifs_error_t err = CIFS_OK;
> if (wd->recv_data == false)
> if (buf != wd->u.data_buf)
> memcpy(buf, wd->u.data_buf, n);
> bytes_read = 0;
> while(bytes_read != n)
> read_ret = read(wd->u.rfd, buf + bytes_read, n - bytes_read);
> if (read_ret == 0)
> read_ret = -1;
> CIFS_NOTICE("%s: Short read from socket, n %ld, bytes_read %ld,"
> " errno %d", __FUNCTION__, n, bytes_read, errno);
> if (errno == 0)
> errno = EIO;
> if (read_ret == -1)
> if (errno == EINTR)
> if(num_continuous_interupts > 100)
> errno =* EIO;*
> *<==== This is the EIO error I was speaking about*
> err = ERRNO_TO_CIFS_ERROR(errno);
> CIFS_ERROR_DONE(err, "%s: Error reading file data from socket",
> bytes_read += read_ret;
> assert(bytes_read == n);
> return err;
> On Thu, Sep 18, 2014 at 10:17 AM, Richard Sharpe <
> realrichardsharpe at gmail.com> wrote:
> > On Thu, Sep 18, 2014 at 10:08 AM, Volker Lendecke
> > <Volker.Lendecke at sernet.de> wrote:
> > > Hi!
> > >
> > > Windows servers expect writes to succeed unless there's a
> > > real error like a full disk or permission denied or so.
> > > There won't be a retry. The retry logic needs to live within
> > > smbd completely.
> > >
> > > For a VFS that goes out to a socket and not to a local
> > > syscall, I would recommend that you look at our async I/O.
> > > With Samba 4.1 we have implemented very flexible VFS
> > > operations (pread_send/recv and pwrite_send/recv) that are
> > > able to handle this nicely. In case you're sitting on an
> > > earlier version, you need to take a look at
> > > aio_read/aio_write/aio_return. Not as flexibile, but you can
> > > also implement async retry logic there.
> > >
> > > It would be best if you would post your VFS module source
> > > somewhere (it's GPL in the end :-)) so that we can make
> > > recommendations.
> > What he didn't tell you is that it is Samba 3.5.15 or so and they are
> > using the Async IO stuff in that version.
> > --
> > Regards,
> > Richard Sharpe
> > (何以解憂？唯有杜康。--曹操)
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