rgw: allow protocol bucket listing default max to override config max

The config option "rgw_max_listing_results" sets a maximum listing
count across a number of operations. Some protocols define a default
listing count for some operations. For example, Swift defines a
default container listing count of 10,000 items. When this protocol
default exceeds the number defined in the config option, the default
value should be considered the actual maximum allowed.

Signed-off-by: J. Eric Ivancich <ivancich@redhat.com>

src/common/options.cc

@@ -6935,8 +6935,9 @@ std::vector<Option> get_rgw_options() {
     .set_default(1000)
     .set_min_max(1, 100000)
     .add_service("rgw")
-    .set_description("Upper bound on results in listing operations, ListBucket max-keys")
+    .set_description("Upper-bound on results in listing operations, ListBucket max-keys")
     .set_long_description("This caps the maximum permitted value for listing-like operations in RGW S3. "
+			  "Swift overrides this to 10000 for bucket listing. "
 			  "Affects ListBucket(max-keys), "
 			  "ListBucketVersions(max-keys), "
 			  "ListBucketMultipartUploads(max-uploads), "

src/rgw/rgw_op.cc

@@ -2888,9 +2888,12 @@ int RGWListBucket::parse_max_keys()
   // Bound min value of max-keys to '0'
   // Some S3 clients explicitly send max-keys=0 to detect if the bucket is
   // empty without listing any items.
-  return parse_value_and_bound(max_keys, max, 0,
-			g_conf().get_val<uint64_t>("rgw_max_listing_results"),
-			default_max);
+  return parse_value_and_bound(max_keys, // input string
+			       max, // output int
+			       0, // lower-bound
+			       g_conf().get_val<uint64_t>("rgw_max_listing_results"), // upper-bound
+			       default_max // default value
+    );
 }
 
 void RGWListBucket::pre_exec()

src/rgw/rgw_op.h

@@ -2458,17 +2458,30 @@ static inline int parse_value_and_bound(
     char *endptr;
     output = strtol(input.c_str(), &endptr, 10);
     if (endptr) {
-      if (endptr == input.c_str()) return -EINVAL;
-      while (*endptr && isspace(*endptr)) // ignore white space
+      if (endptr == input.c_str()) {
+	// if no numeric characters, invalid input
+	return -EINVAL;
+      }
+      while (*endptr && isspace(*endptr)) { // ignore white space
         endptr++;
+      }
       if (*endptr) {
+	// if after skipping white-space we're not at the null
+	// terminating character, then there are one/more illegal
+	// characters
         return -EINVAL;
       }
     }
-    if(output > upper_bound) {
-      output = upper_bound;
+
+    // if the default values is greater than the upper-bound, it
+    // becomes the upper-bound; for example, Swift's default value for
+    // bucket listing is 10,000
+    const long true_upper_bound = std::max(upper_bound, default_val);
+
+    if (output > true_upper_bound) {
+      output = true_upper_bound;
     }
-    if(output < lower_bound) {
+    if (output < lower_bound) {
       output = lower_bound;
     }
   } else {