Question on continuous EIOs in CIFS protocol
sandeepnagamalli at gmail.com
Thu Sep 18 12:28:34 MDT 2014
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()'
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);
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.
> Richard Sharpe
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