On 09/10/2010 12:40 AM, Daniel De Graaf wrote:
> On 09/09/2010 05:27 AM, Jun Zhu (Intern) wrote:
>> Is it related to the following patch? The following patch fixes the problem
>> of queue deletion.
> Yes, this would have caused a zero return due to an empty item being left
> in the queue. It's likely my patch is not needed with this one applied; we
> are already careful to avoid adding zero-length elements to the queue,
> which was my original idea for the cause.
No, that's a separate issue. This patch fixes the case where the
usermode buffer is near a page boundary so the copy to usermode is
truncated.
Anyway, I've applied both.
J
>> diff --git a/drivers/xen/xenfs/xenbus.c b/drivers/xen/xenfs/xenbus.c
>> index 64b3be4..763e90d 100644
>> --- a/drivers/xen/xenfs/xenbus.c
>> +++ b/drivers/xen/xenfs/xenbus.c
>> @@ -143,7 +143,7 @@ static ssize_t xenbus_file_read(struct file *filp,
>> i += sz - ret;
>> rb->cons += sz - ret;
>>
>> - if (ret != sz) {
>> + if (ret != 0) {
>> if (i == 0)
>> i = -EFAULT;
>> goto out;
>>
>> Jun Zhu
>> Citrix Systems UK
>> ________________________________________
>> From: Daniel De Graaf [dgdegra@xxxxxxxxxxxxx]
>> Sent: 08 September 2010 18:10
>> To: Jeremy Fitzhardinge
>> Cc: xen-devel; Jun Zhu (Intern)
>> 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 <dgdegra@xxxxxxxxxxxxx>
>>
>> ---
>> diff --git a/drivers/xen/xenfs/xenbus.c b/drivers/xen/xenfs/xenbus.c
>> index 88c87c9..0ddef43 100644
>> --- a/drivers/xen/xenfs/xenbus.c
>> +++ b/drivers/xen/xenfs/xenbus.c
>> @@ -121,6 +121,7 @@ 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)
>> @@ -159,6 +160,8 @@ static ssize_t xenbus_file_read(struct file *filp,
>> struct read_buffer, list);
>> }
>> }
>> + if (i == 0)
>> + goto again;
>>
>> out:
>> mutex_unlock(&u->reply_mutex);
>
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