On 2/2/21 01:38, Christoph Hellwig wrote:

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

quoted

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.

I didn't find anything in the spec that says we need to return the
the status of 0 for unallocated [1] NSID.

I've checked with two different PCIe controllers for id-ns with invalid
nsid they both returned NVME_SC_INVALID_NS and so does QEMU :-

PCIe:-

# nvme list | tr -s ' ' ' '
Node SN Model Namespace Usage Format FW Rev
/dev/nvme0n1 191515805865 XXXXXXXXXXX-00SJG0 1 250.06 GB / 250.06 GB 512
B + 0 B 102000XX
/dev/nvme1n1 191912800089 XXXXXXXXXXX-00SJG0 1 2.00 TB / 2.00 TB 512 B +
0 B 102430XX

# nvme id-ns /dev/nvme0n1 -n 100
NVMe Status:INVALID_NS(400b) NSID:100

# nvme id-ns /dev/nvme1n1 -n 100
NVMe Status:INVALID_NS(400b) NSID:100

QEMU:-

# nvme list | tr -s ' ' ' '
Node SN Model Namespace Usage Format FW Rev
/dev/nvme0n1 foo QEMU NVMe Ctrl 1 1.07 GB / 1.07 GB 512 B + 0 B 1.0
# nvme id-ns /dev/nvme0 -n 100
NVMe status: INVALID_NS: The namespace or the format of that namespace
is invalid(0x400b)

Without bffcd507780e targetwas returning success and zeroed buffer [2].
Now with bffcd507780etarget is returning NVME_SC_INVALID but the buffer
is not
zeroed (which was there in original patch [3] then we changed to not copy
buffer [4]). Above call to nvmet_zero_sgl() in this patch fixes that.

Please correct me if I missed something.

quoted

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.

[1] Unallocated NSIDs do not refer to any namespaces that exist in the
NVM subsystem.
[2] http://lists.infradead.org/pipermail/linux-nvme/2021-January/021954.html
[3] http://lists.infradead.org/pipermail/linux-nvme/2021-January/021954.html
[4] http://lists.infradead.org/pipermail/linux-nvme/2021-January/021979.html

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