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xenbus: avoid zero returns from read()

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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 <dgdegra@tycho.nsa.gov>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
This commit is contained in:
Daniel De Graaf 2010-09-08 18:10:42 -04:00 committed by Jeremy Fitzhardinge
parent 76ce7618f9
commit 7808121b9a
1 changed files with 3 additions and 0 deletions
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3
drivers/xen/xenfs/xenbus.c
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@ -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);