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Message-ID: <5094296B.5030406@citrix.com>
Date: Fri, 2 Nov 2012 21:13:31 +0100
From: Roger Pau Monné <roger.pau@...rix.com>
To: Konrad Rzeszutek Wilk <konrad@...nok.org>
CC: "xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xen-blk: persistent-grants fixes
On 02/11/12 18:05, Konrad Rzeszutek Wilk wrote:
> On Fri, Nov 02, 2012 at 04:43:04PM +0100, Roger Pau Monne wrote:
>> This patch contains fixes for persistent grants implementation v2:
>>
>> * handle == 0 is a valid handle, so initialize grants in blkback
>> setting the handle to BLKBACK_INVALID_HANDLE instead of 0. Reported
>> by Konrad Rzeszutek Wilk.
>>
>> * new_map is a boolean, use "true" or "false" instead of 1 and 0.
>> Reported by Konrad Rzeszutek Wilk.
>>
>> * blkfront announces the persistent-grants feature as
>> feature-persistent-grants, use feature-persistent instead which is
>> consistent with blkback and the public Xen headers.
>>
>> * Add a consistency check in blkfront to make sure we don't try to
>> access segments that have not been set.
>
> Looks good.. but
>>
>> Signed-off-by: Roger Pau Monne <roger.pau@...rix.com>
>> Cc: <konrad.wilk@...cle.com>
>> Cc: <linux-kernel@...r.kernel.org>
>> ---
>> drivers/block/xen-blkback/blkback.c | 15 +++++++++------
>> drivers/block/xen-blkback/xenbus.c | 2 +-
>> drivers/block/xen-blkfront.c | 3 ++-
>> 3 files changed, 12 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
>> index 663d42d..a059616 100644
>> --- a/drivers/block/xen-blkback/blkback.c
>> +++ b/drivers/block/xen-blkback/blkback.c
>> @@ -503,7 +503,7 @@ static int xen_blkbk_map(struct blkif_request *req,
>> * We are using persistent grants and
>> * the grant is already mapped
>> */
>> - new_map = 0;
>> + new_map = false;
>> } else if (use_persistent_gnts &&
>> blkif->persistent_gnt_c <
>> max_mapped_grant_pages(blkif->blk_protocol)) {
>> @@ -511,8 +511,8 @@ static int xen_blkbk_map(struct blkif_request *req,
>> * We are using persistent grants, the grant is
>> * not mapped but we have room for it
>> */
>> - new_map = 1;
>> - persistent_gnt = kzalloc(
>> + new_map = true;
>> + persistent_gnt = kmalloc(
>
> Why do we want to use kmalloc instead of kzalloc?
In the previous patch I relied on handle being 0 when not set (that's
why I was using kzalloc), but this was wrong (0 is a valid handle), so
now I explicitly initialize it to BLKBACK_INVALID_HANDLE. I replaced the
kzalloc with kmalloc because it should be faster, and there's no need to
zero it anymore.
>
>> sizeof(struct persistent_gnt),
>> GFP_KERNEL);
>> if (!persistent_gnt)
>> @@ -523,6 +523,7 @@ static int xen_blkbk_map(struct blkif_request *req,
>> return -ENOMEM;
>> }
>> persistent_gnt->gnt = req->u.rw.seg[i].gref;
>> + persistent_gnt->handle = BLKBACK_INVALID_HANDLE;
>>
>> pages_to_gnt[segs_to_map] =
>> persistent_gnt->page;
>> @@ -547,7 +548,7 @@ static int xen_blkbk_map(struct blkif_request *req,
>> pr_alert(DRV_PFX " domain %u, device %#x is using maximum number of persistent grants\n",
>> blkif->domid, blkif->vbd.handle);
>> }
>> - new_map = 1;
>> + new_map = true;
>> pages[i] = blkbk->pending_page(pending_req, i);
>> addr = vaddr(pending_req, i);
>> pages_to_gnt[segs_to_map] =
>> @@ -584,7 +585,8 @@ static int xen_blkbk_map(struct blkif_request *req,
>> */
>> bitmap_zero(pending_req->unmap_seg, BLKIF_MAX_SEGMENTS_PER_REQUEST);
>> for (i = 0, j = 0; i < nseg; i++) {
>> - if (!persistent_gnts[i] || !persistent_gnts[i]->handle) {
>> + if (!persistent_gnts[i] ||
>> + persistent_gnts[i]->handle == BLKBACK_INVALID_HANDLE) {
>> /* This is a newly mapped grant */
>> BUG_ON(j >= segs_to_map);
>> if (unlikely(map[j].status != 0)) {
>> @@ -601,7 +603,8 @@ static int xen_blkbk_map(struct blkif_request *req,
>> }
>> }
>> if (persistent_gnts[i]) {
>> - if (!persistent_gnts[i]->handle) {
>> + if (persistent_gnts[i]->handle ==
>> + BLKBACK_INVALID_HANDLE) {
>> /*
>> * If this is a new persistent grant
>> * save the handler
>> diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
>> index b225026..a03ecbb 100644
>> --- a/drivers/block/xen-blkback/xenbus.c
>> +++ b/drivers/block/xen-blkback/xenbus.c
>> @@ -760,7 +760,7 @@ static int connect_ring(struct backend_info *be)
>> return -1;
>> }
>> err = xenbus_gather(XBT_NIL, dev->otherend,
>> - "feature-persistent-grants", "%u",
>> + "feature-persistent", "%u",
>> &pers_grants, NULL);
>> if (err)
>> pers_grants = 0;
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 911d733..f1de806 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -852,6 +852,7 @@ static void blkif_completion(struct blk_shadow *s, struct blkfront_info *info,
>> rq_for_each_segment(bvec, s->request, iter) {
>> BUG_ON((bvec->bv_offset + bvec->bv_len) > PAGE_SIZE);
>> i = offset >> PAGE_SHIFT;
>> + BUG_ON(i >= s->req.u.rw.nr_segments);
>> shared_data = kmap_atomic(
>> pfn_to_page(s->grants_used[i]->pfn));
>> bvec_data = bvec_kmap_irq(bvec, &flags);
>> @@ -1069,7 +1070,7 @@ again:
>> goto abort_transaction;
>> }
>> err = xenbus_printf(xbt, dev->nodename,
>> - "feature-persistent-grants", "%u", 1);
>> + "feature-persistent", "%u", 1);
>> if (err)
>> dev_warn(&dev->dev,
>> "writing persistent grants feature to xenbus");
>> --
>> 1.7.7.5 (Apple Git-26)
>>
>> --
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