btrfs: use feature attribute names to print better error messages

Now that we have the feature name strings available in the kernel via
the sysfs attributes, we can use them for printing better failure
messages from the ioctl path.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

fs/btrfs/ioctl.c

@@ -56,6 +56,7 @@
 #include "rcu-string.h"
 #include "send.h"
 #include "dev-replace.h"
+#include "sysfs.h"
 
 static int btrfs_clone(struct inode *src, struct inode *inode,
 		       u64 off, u64 olen, u64 olen_aligned, u64 destoff);
@@ -4516,33 +4517,57 @@ static int btrfs_ioctl_get_features(struct file *file, void __user *arg)
 	return 0;
 }
 
-static int check_feature_bits(struct btrfs_root *root, const char *type,
+static int check_feature_bits(struct btrfs_root *root,
+			      enum btrfs_feature_set set,
 			      u64 change_mask, u64 flags, u64 supported_flags,
 			      u64 safe_set, u64 safe_clear)
 {
+	const char *type = btrfs_feature_set_names[set];
+	char *names;
 	u64 disallowed, unsupported;
 	u64 set_mask = flags & change_mask;
 	u64 clear_mask = ~flags & change_mask;
 
 	unsupported = set_mask & ~supported_flags;
 	if (unsupported) {
-		btrfs_warn(root->fs_info,
+		names = btrfs_printable_features(set, unsupported);
+		if (names) {
+			btrfs_warn(root->fs_info,
+			   "this kernel does not support the %s feature bit%s",
+			   names, strchr(names, ',') ? "s" : "");
+			kfree(names);
+		} else
+			btrfs_warn(root->fs_info,
 			   "this kernel does not support %s bits 0x%llx",
 			   type, unsupported);
 		return -EOPNOTSUPP;
 	}
 
 	disallowed = set_mask & ~safe_set;
 	if (disallowed) {
-		btrfs_warn(root->fs_info,
+		names = btrfs_printable_features(set, disallowed);
+		if (names) {
+			btrfs_warn(root->fs_info,
+			   "can't set the %s feature bit%s while mounted",
+			   names, strchr(names, ',') ? "s" : "");
+			kfree(names);
+		} else
+			btrfs_warn(root->fs_info,
 			   "can't set %s bits 0x%llx while mounted",
 			   type, disallowed);
 		return -EPERM;
 	}
 
 	disallowed = clear_mask & ~safe_clear;
 	if (disallowed) {
-		btrfs_warn(root->fs_info,
+		names = btrfs_printable_features(set, disallowed);
+		if (names) {
+			btrfs_warn(root->fs_info,
+			   "can't clear the %s feature bit%s while mounted",
+			   names, strchr(names, ',') ? "s" : "");
+			kfree(names);
+		} else
+			btrfs_warn(root->fs_info,
 			   "can't clear %s bits 0x%llx while mounted",
 			   type, disallowed);
 		return -EPERM;
@@ -4552,7 +4577,7 @@ static int check_feature_bits(struct btrfs_root *root, const char *type,
 }
 
 #define check_feature(root, change_mask, flags, mask_base)	\
-check_feature_bits(root, # mask_base, change_mask, flags,	\
+check_feature_bits(root, FEAT_##mask_base, change_mask, flags,	\
 		   BTRFS_FEATURE_ ## mask_base ## _SUPP,	\
 		   BTRFS_FEATURE_ ## mask_base ## _SAFE_SET,	\
 		   BTRFS_FEATURE_ ## mask_base ## _SAFE_CLEAR)

fs/btrfs/sysfs.c

@@ -254,6 +254,31 @@ const char * const btrfs_feature_set_names[3] = {
 static char btrfs_unknown_feature_names[3][NUM_FEATURE_BITS][13];
 static struct btrfs_feature_attr btrfs_feature_attrs[3][NUM_FEATURE_BITS];
 
+char *btrfs_printable_features(enum btrfs_feature_set set, u64 flags)
+{
+	size_t bufsize = 4096; /* safe max, 64 names * 64 bytes */
+	int len = 0;
+	int i;
+	char *str;
+
+	str = kmalloc(bufsize, GFP_KERNEL);
+	if (!str)
+		return str;
+
+	for (i = 0; i < ARRAY_SIZE(btrfs_feature_attrs[set]); i++) {
+		const char *name;
+
+		if (!(flags & (1ULL << i)))
+			continue;
+
+		name = btrfs_feature_attrs[set][i].kobj_attr.attr.name;
+		len += snprintf(str + len, bufsize - len, "%s%s",
+				len ? "," : "", name);
+	}
+
+	return str;
+}
+
 static void init_feature_attrs(void)
 {
 	struct btrfs_feature_attr *fa;
@@ -264,11 +289,17 @@ static void init_feature_attrs(void)
 	BUILD_BUG_ON(ARRAY_SIZE(btrfs_unknown_feature_names[0]) !=
 		     ARRAY_SIZE(btrfs_feature_attrs[0]));
 
+	memset(btrfs_feature_attrs, 0, sizeof(btrfs_feature_attrs));
+	memset(btrfs_unknown_feature_names, 0,
+	       sizeof(btrfs_unknown_feature_names));
+
 	for (i = 0; btrfs_supported_feature_attrs[i]; i++) {
 		struct btrfs_feature_attr *sfa;
 		struct attribute *a = btrfs_supported_feature_attrs[i];
+		int bit;
 		sfa = attr_to_btrfs_feature_attr(a);
-		fa = &btrfs_feature_attrs[sfa->feature_set][sfa->feature_bit];
+		bit = ilog2(sfa->feature_bit);
+		fa = &btrfs_feature_attrs[sfa->feature_set][bit];
 
 		fa->kobj_attr.attr.name = sfa->kobj_attr.attr.name;
 	}

fs/btrfs/sysfs.h

@@ -51,4 +51,6 @@ static struct btrfs_feature_attr btrfs_attr_##_name = {			     \
 #define attr_to_btrfs_attr(a) container_of(a, struct kobj_attribute, attr)
 #define attr_to_btrfs_feature_attr(a) \
 			to_btrfs_feature_attr(attr_to_btrfs_attr(a))
+char *btrfs_printable_features(enum btrfs_feature_set set, u64 flags);
+extern const char * const btrfs_feature_set_names[3];
 #endif /* _BTRFS_SYSFS_H_ */