On Tue, Feb 02, 2021 at 12:12:33AM +0000, Chaitanya Kulkarni wrote:

quoted

quoted

+	req->ns = nvmet_find_namespace(ctrl, req->cmd->identify.nsid);
+	if (!req->ns) {
+		status = NVME_SC_INVALID_NS;
+		/*
+		 * According to spec : If the specified namespace is
+		 * an unallocated NSID then the controller returns a zero filled
+		 * data structure. Also don't override the error status as invalid
+		 * namespace takes priority over the failed zeroout buffer case.
+		 */
+		nvmet_zero_sgl(req, 0, sizeof(*id));
+		goto out;
+	}
+
 	id = kzalloc(sizeof(*id), GFP_KERNEL);
 	if (!id) {
 		status = NVME_SC_INTERNAL;
 		goto out;
 	}
 
-	/* return an all zeroed buffer if we can't find an active namespace */
-	req->ns = nvmet_find_namespace(ctrl, req->cmd->identify.nsid);
-	if (!req->ns) {
-		status = NVME_SC_INVALID_NS;
-		goto done;

I think all we need to do is to remove the status assignment here.
While you're patch avoids the memory allocation for this case, it isn't
really the fast path so I'd rather avoid the extra code.

Sorry, I didn't understand this comment. If we remove the status assignment
then host will not get the right error. That is the bug we fixed it
initially
with bffcd507780e.

Actually, looking at it, bffcd507780e is wrong.  Identify Namespace
to a namespace that is not active should return a status of 0 and
a zeroed structure.

Regarding fast path, if system is under pressure even single memory
allocation
can be costly, especially when host tries to do read id-ns, is there any
reason why we should not consider this scenario ?

No sensible host gets there.  I'd rather keep the code simple.

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