From 7808121b9a1e44ef12fecd49fa6c268f27a150fc Mon Sep 17 00:00:00 2001 From: Daniel De Graaf Date: Wed, 8 Sep 2010 18:10:42 -0400 Subject: [PATCH] xenbus: avoid zero returns from read() It is possible to get a zero return from read() in instances where the queue is not empty but has no elements with data to deliver to the user. Since a zero return from read is an error indicator, resume waiting or return -EAGAIN (for a nonblocking fd) in this case. Signed-off-by: Daniel De Graaf Signed-off-by: Jeremy Fitzhardinge --- drivers/xen/xenfs/xenbus.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/drivers/xen/xenfs/xenbus.c b/drivers/xen/xenfs/xenbus.c index c4c7db8..55791dd 100644 --- a/drivers/xen/xenfs/xenbus.c +++ b/drivers/xen/xenfs/xenbus.c @@ -120,6 +120,7 @@ static ssize_t xenbus_file_read(struct file *filp, int ret; mutex_lock(&u->reply_mutex); +again: while (list_empty(&u->read_buffers)) { mutex_unlock(&u->reply_mutex); if (filp->f_flags & O_NONBLOCK) @@ -158,6 +159,8 @@ static ssize_t xenbus_file_read(struct file *filp, struct read_buffer, list); } } + if (i == 0) + goto again; out: mutex_unlock(&u->reply_mutex); -- 2.7.4