Re: [PATCH v4 03/10] KVM: selftests: Read binary stats desc in lib

[Sean Christopherson <seanjc@google.com>]

On Tue, Apr 12, 2022, Sean Christopherson wrote:
> On Tue, Apr 12, 2022, Ben Gardon wrote:
> > On Mon, Apr 11, 2022 at 5:55 PM Mingwei Zhang <mizhang@google.com> wrote:
> > > I was very confused on header->name_size. So this field means the
> > > maximum string size of a stats name, right? Can we update the comments
> > > in the kvm.h to specify that? By reading the comments, I don't really
> > > feel this is how we should use this field.
> > 
> > I believe that's right. I agree the documentation on that was a little
> > confusing.
> 
> Heh, a little.  I got tripped up looking at this too.  Give me a few minutes and
> I'll attach a cleanup patch to add comments and fix the myriad style issues.
> 
> This whole file is painful to look at.  Aside from violating preferred kernel
> style, it's horribly consistent with itself.  Well, except for the 80 char limit,
> to which it has a fanatical devotion.

If you send a new version of this series, can you add this on top?

From: Sean Christopherson <seanjc@google.com>
Date: Tue, 12 Apr 2022 11:49:59 -0700
Subject: [PATCH] KVM: selftests: Clean up coding style in binary stats test

Fix a variety of code style violations and/or inconsistencies in the
binary stats test.  The 80 char limit is a soft limit and can and should
be ignored/violated if doing so improves the overall code readability.

Specifically, provide consistent indentation and don't split expressions
at arbitrary points just to honor the 80 char limit.

Opportunistically expand/add comments to call out the more subtle aspects
of the code.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 .../selftests/kvm/kvm_binary_stats_test.c     | 91 ++++++++++++-------
 1 file changed, 56 insertions(+), 35 deletions(-)

diff --git a/tools/testing/selftests/kvm/kvm_binary_stats_test.c b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
index 97b180249ba0..944ed52e3f07 100644
--- a/tools/testing/selftests/kvm/kvm_binary_stats_test.c
+++ b/tools/testing/selftests/kvm/kvm_binary_stats_test.c
@@ -37,32 +37,42 @@ static void stats_test(int stats_fd)
 	/* Read kvm stats header */
 	read_vm_stats_header(stats_fd, &header);

+	/*
+	 * The base size of the descriptor is defined by KVM's ABI, but the
+	 * size of the name field is variable as far as KVM's ABI is concerned.
+	 * But, the size of name is constant for a given instance of KVM and
+	 * is provided by KVM in the overall stats header.
+	 */
 	size_desc = sizeof(*stats_desc) + header.name_size;

 	/* Read kvm stats id string */
 	id = malloc(header.name_size);
 	TEST_ASSERT(id, "Allocate memory for id string");
+
 	ret = read(stats_fd, id, header.name_size);
 	TEST_ASSERT(ret == header.name_size, "Read id string");

 	/* Check id string, that should start with "kvm" */
 	TEST_ASSERT(!strncmp(id, "kvm", 3) && strlen(id) < header.name_size,
-				"Invalid KVM stats type, id: %s", id);
+		    "Invalid KVM stats type, id: %s", id);

 	/* Sanity check for other fields in header */
 	if (header.num_desc == 0) {
 		printf("No KVM stats defined!");
 		return;
 	}
-	/* Check overlap */
-	TEST_ASSERT(header.desc_offset > 0 && header.data_offset > 0
-			&& header.desc_offset >= sizeof(header)
-			&& header.data_offset >= sizeof(header),
-			"Invalid offset fields in header");
+	/*
+	 * The descriptor and data offsets must be valid, they must not overlap
+	 * the header, and the descriptor and data blocks must not overlap each
+	 * other.  Note, the data block is rechecked after its size is known.
+	 */
+	TEST_ASSERT(header.desc_offset && header.desc_offset >= sizeof(header) &&
+		    header.data_offset && header.data_offset >= sizeof(header),
+		    "Invalid offset fields in header");
+
 	TEST_ASSERT(header.desc_offset > header.data_offset ||
-			(header.desc_offset + size_desc * header.num_desc <=
-							header.data_offset),
-			"Descriptor block is overlapped with data block");
+		    (header.desc_offset + size_desc * header.num_desc <= header.data_offset),
+		    "Descriptor block is overlapped with data block");

 	/* Read kvm stats descriptors */
 	stats_desc = alloc_vm_stats_desc(stats_fd, &header);
@@ -70,15 +80,22 @@ static void stats_test(int stats_fd)

 	/* Sanity check for fields in descriptors */
 	for (i = 0; i < header.num_desc; ++i) {
+		/*
+		 * Note, size_desc includes the of the name field, which is
+		 * variable, i.e. this is NOT equivalent to &stats_desc[i].
+		 */
 		pdesc = (void *)stats_desc + i * size_desc;
-		/* Check type,unit,base boundaries */
-		TEST_ASSERT((pdesc->flags & KVM_STATS_TYPE_MASK)
-				<= KVM_STATS_TYPE_MAX, "Unknown KVM stats type");
-		TEST_ASSERT((pdesc->flags & KVM_STATS_UNIT_MASK)
-				<= KVM_STATS_UNIT_MAX, "Unknown KVM stats unit");
-		TEST_ASSERT((pdesc->flags & KVM_STATS_BASE_MASK)
-				<= KVM_STATS_BASE_MAX, "Unknown KVM stats base");
-		/* Check exponent for stats unit
+
+		/* Check type, unit, and base boundaries */
+		TEST_ASSERT((pdesc->flags & KVM_STATS_TYPE_MASK) <= KVM_STATS_TYPE_MAX,
+			    "Unknown KVM stats type");
+		TEST_ASSERT((pdesc->flags & KVM_STATS_UNIT_MASK) <= KVM_STATS_UNIT_MAX,
+			    "Unknown KVM stats unit");
+		TEST_ASSERT((pdesc->flags & KVM_STATS_BASE_MASK) <= KVM_STATS_BASE_MAX,
+			    "Unknown KVM stats base");
+
+		/*
+		 * Check exponent for stats unit
 		 * Exponent for counter should be greater than or equal to 0
 		 * Exponent for unit bytes should be greater than or equal to 0
 		 * Exponent for unit seconds should be less than or equal to 0
@@ -89,47 +106,51 @@ static void stats_test(int stats_fd)
 		case KVM_STATS_UNIT_NONE:
 		case KVM_STATS_UNIT_BYTES:
 		case KVM_STATS_UNIT_CYCLES:
-			TEST_ASSERT(pdesc->exponent >= 0,
-					"Unsupported KVM stats unit");
+			TEST_ASSERT(pdesc->exponent >= 0, "Unsupported KVM stats unit");
 			break;
 		case KVM_STATS_UNIT_SECONDS:
-			TEST_ASSERT(pdesc->exponent <= 0,
-					"Unsupported KVM stats unit");
+			TEST_ASSERT(pdesc->exponent <= 0, "Unsupported KVM stats unit");
 			break;
 		}
 		/* Check name string */
 		TEST_ASSERT(strlen(pdesc->name) < header.name_size,
-				"KVM stats name(%s) too long", pdesc->name);
+			    "KVM stats name(%s) too long", pdesc->name);
 		/* Check size field, which should not be zero */
-		TEST_ASSERT(pdesc->size, "KVM descriptor(%s) with size of 0",
-				pdesc->name);
+		TEST_ASSERT(pdesc->size,
+			    "KVM descriptor(%s) with size of 0", pdesc->name);
 		/* Check bucket_size field */
 		switch (pdesc->flags & KVM_STATS_TYPE_MASK) {
 		case KVM_STATS_TYPE_LINEAR_HIST:
 			TEST_ASSERT(pdesc->bucket_size,
-			    "Bucket size of Linear Histogram stats (%s) is zero",
-			    pdesc->name);
+				    "Bucket size of Linear Histogram stats (%s) is zero",
+				    pdesc->name);
 			break;
 		default:
 			TEST_ASSERT(!pdesc->bucket_size,
-			    "Bucket size of stats (%s) is not zero",
-			    pdesc->name);
+				    "Bucket size of stats (%s) is not zero",
+				    pdesc->name);
 		}
 		size_data += pdesc->size * sizeof(*stats_data);
 	}
-	/* Check overlap */
-	TEST_ASSERT(header.data_offset >= header.desc_offset
-		|| header.data_offset + size_data <= header.desc_offset,
-		"Data block is overlapped with Descriptor block");
+
+	/*
+	 * Now that the size of the data block is known, verify the data block
+	 * doesn't overlap the descriptor block.
+	 */
+	TEST_ASSERT(header.data_offset >= header.desc_offset ||
+		    header.data_offset + size_data <= header.desc_offset,
+		    "Data block is overlapped with Descriptor block");
+
 	/* Check validity of all stats data size */
 	TEST_ASSERT(size_data >= header.num_desc * sizeof(*stats_data),
-			"Data size is not correct");
+		    "Data size is not correct");
+
 	/* Check stats offset */
 	for (i = 0; i < header.num_desc; ++i) {
 		pdesc = (void *)stats_desc + i * size_desc;
 		TEST_ASSERT(pdesc->offset < size_data,
-			"Invalid offset (%u) for stats: %s",
-			pdesc->offset, pdesc->name);
+			    "Invalid offset (%u) for stats: %s",
+			    pdesc->offset, pdesc->name);
 	}

 	/* Read kvm stats data one by one */

base-commit: f9955a6aaa037a7a8198a817b9d272efcf10961a
--