linux-kernel - [PATCH 4/6] staging: comedi: don't allocate buffer space when polling for write

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Message-Id: <1444390012-6980-5-git-send-email-abbotti@mev.co.uk>
Date:	Fri,  9 Oct 2015 12:26:50 +0100
From:	Ian Abbott <abbotti@....co.uk>
To:	driverdev-devel@...uxdriverproject.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ian Abbott <abbotti@....co.uk>,
	H Hartley Sweeten <hsweeten@...ionengravers.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH 4/6] staging: comedi: don't allocate buffer space when polling for write

When handling the "poll" file operation and checking for `POLLOUT`,
don't allocate space from the buffer for writing, just check that space
is available for writing.  That check is done after checking that an
asynchronous "write" command is running on the subdevice.  Allocating
the buffer space before checking a "write" command is running can cause
problems if the subdevice supports commands in either direction and
currently has an active "read" command.

Signed-off-by: Ian Abbott <abbotti@....co.uk>
---
 drivers/staging/comedi/comedi_fops.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index 9dcd486..4793e30 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2287,10 +2287,9 @@ static unsigned int comedi_poll(struct file *file, poll_table *wait)
 
 		if (s != s_read)
 			poll_wait(file, &s->async->wait_head, wait);
-		comedi_buf_write_alloc(s, s->async->prealloc_bufsz);
 		if (!s->busy || !comedi_is_subdevice_running(s) ||
 		    !(s->async->cmd.flags & CMDF_WRITE) ||
-		    comedi_buf_write_n_allocated(s) >= bps)
+		    comedi_buf_write_n_available(s) >= bps)
 			mask |= POLLOUT | POLLWRNORM;
 	}
 
-- 
2.6.1

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