Question on continuous EIOs in CIFS protocol

[sandeep nag]

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
cifs_wd_to_buf(
    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);
        }
        CIFS_DONE();
    }

    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)
            {
                num_continuous_interupts++;
                if(num_continuous_interupts > 100)
                {
                    errno =* EIO;*
                   *<====  This is the EIO error I was speaking about*
                }
                else
                    continue;
            }

            assert(errno);
            err = ERRNO_TO_CIFS_ERROR(errno);
            CIFS_ERROR_DONE(err, "%s: Error reading file data from socket",
                                __FUNCTION__);
        }

        bytes_read += read_ret;
    }

    assert(bytes_read == n);

done:
    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)
>