Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1244880 > unrolled thread

[PATCH 06/10] staging: comedi: allow buffer wraparound in comedi_read()

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  [PATCH 06/10] staging: comedi: allow buffer wraparound in comedi_read() Ian Abbott <abbotti@mev.co.uk> - 2015-10-12 18:30 +0200

#1244880 — [PATCH 06/10] staging: comedi: allow buffer wraparound in comedi_read()

`comedi_read()` copies data from the acquisition data buffer, which is
cyclic, to the user buffer using a single call to `copy_to_user()`.  It
currently avoids having to deal with wraparound of the cyclic buffer by
limiting the amount it copies (and the amount returned to the user).
Change it to deal with the wraparound using two calls to
`copy_to_user()` if necessary.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
---
 drivers/staging/comedi/comedi_fops.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/comedi/comedi_fops.c b/drivers/staging/comedi/comedi_fops.c
index d51c94c..b534b49 100644
--- a/drivers/staging/comedi/comedi_fops.c
+++ b/drivers/staging/comedi/comedi_fops.c
@@ -2490,11 +2490,11 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 
 	add_wait_queue(&async->wait_head, &wait);
 	while (nbytes > 0 && !retval) {
+		unsigned int rp, n1, n2;
+
 		set_current_state(TASK_INTERRUPTIBLE);
 
 		m = comedi_buf_read_n_available(s);
-		if (async->buf_read_ptr + m > async->prealloc_bufsz)
-			m = async->prealloc_bufsz - async->buf_read_ptr;
 		n = min_t(size_t, m, nbytes);
 
 		if (n == 0) {
@@ -2531,8 +2531,14 @@ static ssize_t comedi_read(struct file *file, char __user *buf, size_t nbytes,
 			}
 			continue;
 		}
-		m = copy_to_user(buf, async->prealloc_buf +
-				 async->buf_read_ptr, n);
+		rp = async->buf_read_ptr;
+		n1 = min(n, async->prealloc_bufsz - rp);
+		n2 = n - n1;
+		m = copy_to_user(buf, async->prealloc_buf + rp, n1);
+		if (m)
+			m += n2;
+		else if (n2)
+			m = copy_to_user(buf + n1, async->prealloc_buf, n2);
 		if (m) {
 			n -= m;
 			retval = -EFAULT;
-- 
2.6.1

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

[toc] | [standalone]

Back to top | Article view | linux.kernel

csiph-web