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Re: [Qemu-devel] [Xen-devel] [PATCH 2/2] xen: dont try setting max grant
From: |
Juergen Gross |
Subject: |
Re: [Qemu-devel] [Xen-devel] [PATCH 2/2] xen: dont try setting max grants multiple times |
Date: |
Fri, 22 Sep 2017 14:03:47 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 |
On 20/09/17 17:00, Anthony PERARD wrote:
> On Tue, Sep 19, 2017 at 01:50:55PM +0200, Juergen Gross wrote:
>> Trying to call xengnttab_set_max_grants() with the same file handle
>> might fail on some kernels, as this operation is allowed only once.
>>
>> This is a problem for the qdisk backend as blk_connect() can be
>> called multiple times for a domain, e.g. in case grub-xen is being
>> used to boot it.
>>
>> So instead of letting the generic backend code open the gnttab device
>> do it in blk_connect() and close it again in blk_disconnect.
>>
>> Signed-off-by: Juergen Gross <address@hidden>
>> ---
>> hw/block/xen_disk.c | 12 +++++++++++-
>> 1 file changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
>> index 6632746250..7cff8863cb 100644
>> --- a/hw/block/xen_disk.c
>> +++ b/hw/block/xen_disk.c
>> @@ -1220,6 +1220,12 @@ static int blk_connect(struct XenDevice *xendev)
>> /* Add on the number needed for the ring pages */
>> max_grants += blkdev->nr_ring_ref;
>>
>> + blkdev->xendev.gnttabdev = xengnttab_open(NULL, 0);
>> + if (blkdev->xendev.gnttabdev == NULL) {
>> + xen_pv_printf(xendev, 0, "xengnttab_open failed: %s\n",
>> + strerror(errno));
>> + return -1;
>> + }
>> if (xengnttab_set_max_grants(blkdev->xendev.gnttabdev, max_grants)) {
>> xen_pv_printf(xendev, 0, "xengnttab_set_max_grants failed: %s\n",
>> strerror(errno));
>> @@ -1327,6 +1333,11 @@ static void blk_disconnect(struct XenDevice *xendev)
>> }
>> blkdev->feature_persistent = false;
>> }
>> +
>> + if (blkdev->xendev.gnttabdev) {
>> + xengnttab_close(blkdev->xendev.gnttabdev);
>> + blkdev->xendev.gnttabdev = NULL;
>> + }
>
> I think blk_disconnect needs to be called from blk_free in case where
> the gnttabdev is not closed (like it is done when blk or the sring are
> not cleared, in blk_free).
Right. Just calling it always from blk_free() should do the job.
BTW: in practice this wouldn't be necessary as xen_pv_del_xendev()
already does the close, but this is just good luck. Better closing it
via blk_free() in case xen_pv_del_xendev() adds a test for
DEVOPS_FLAG_NEED_GNTDEV.
Thanks,
Juergen