ext4: factor out ext4_xattr_credits_for_new_inode()

To compute a new inode's xattr credits, we need to know whether the
inode will be encrypted or not.  When we switch to use the new helper
function fscrypt_prepare_new_inode(), we won't find out whether the
inode will be encrypted until slightly later than is currently the case.
That will require moving the code block that computes the xattr credits.

To make this easier and reduce the length of __ext4_new_inode(), move
this code block into a new function ext4_xattr_credits_for_new_inode().

Link: https://lore.kernel.org/r/20200917041136.178600-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>

fs/ext4/ialloc.c

@@ -742,6 +742,53 @@ not_found:
 	return 1;
 }
 
+static int ext4_xattr_credits_for_new_inode(struct inode *dir, mode_t mode,
+					    bool encrypt)
+{
+	struct super_block *sb = dir->i_sb;
+	int nblocks = 0;
+#ifdef CONFIG_EXT4_FS_POSIX_ACL
+	struct posix_acl *p = get_acl(dir, ACL_TYPE_DEFAULT);
+
+	if (IS_ERR(p))
+		return PTR_ERR(p);
+	if (p) {
+		int acl_size = p->a_count * sizeof(ext4_acl_entry);
+
+		nblocks += (S_ISDIR(mode) ? 2 : 1) *
+			__ext4_xattr_set_credits(sb, NULL /* inode */,
+						 NULL /* block_bh */, acl_size,
+						 true /* is_create */);
+		posix_acl_release(p);
+	}
+#endif
+
+#ifdef CONFIG_SECURITY
+	{
+		int num_security_xattrs = 1;
+
+#ifdef CONFIG_INTEGRITY
+		num_security_xattrs++;
+#endif
+		/*
+		 * We assume that security xattrs are never more than 1k.
+		 * In practice they are under 128 bytes.
+		 */
+		nblocks += num_security_xattrs *
+			__ext4_xattr_set_credits(sb, NULL /* inode */,
+						 NULL /* block_bh */, 1024,
+						 true /* is_create */);
+	}
+#endif
+	if (encrypt)
+		nblocks += __ext4_xattr_set_credits(sb,
+						    NULL /* inode */,
+						    NULL /* block_bh */,
+						    FSCRYPT_SET_CONTEXT_MAX_SIZE,
+						    true /* is_create */);
+	return nblocks;
+}
+
 /*
  * There are two policies for allocating an inode.  If the new inode is
  * a directory, then a forward search is made for a block group with both
@@ -796,45 +843,10 @@ struct inode *__ext4_new_inode(handle_t *handle, struct inode *dir,
 	}
 
 	if (!handle && sbi->s_journal && !(i_flags & EXT4_EA_INODE_FL)) {
-#ifdef CONFIG_EXT4_FS_POSIX_ACL
-		struct posix_acl *p = get_acl(dir, ACL_TYPE_DEFAULT);
-
-		if (IS_ERR(p))
-			return ERR_CAST(p);
-		if (p) {
-			int acl_size = p->a_count * sizeof(ext4_acl_entry);
-
-			nblocks += (S_ISDIR(mode) ? 2 : 1) *
-				__ext4_xattr_set_credits(sb, NULL /* inode */,
-					NULL /* block_bh */, acl_size,
-					true /* is_create */);
-			posix_acl_release(p);
-		}
-#endif
-
-#ifdef CONFIG_SECURITY
-		{
-			int num_security_xattrs = 1;
-
-#ifdef CONFIG_INTEGRITY
-			num_security_xattrs++;
-#endif
-			/*
-			 * We assume that security xattrs are never
-			 * more than 1k.  In practice they are under
-			 * 128 bytes.
-			 */
-			nblocks += num_security_xattrs *
-				__ext4_xattr_set_credits(sb, NULL /* inode */,
-					NULL /* block_bh */, 1024,
-					true /* is_create */);
-		}
-#endif
-		if (encrypt)
-			nblocks += __ext4_xattr_set_credits(sb,
-					NULL /* inode */, NULL /* block_bh */,
-					FSCRYPT_SET_CONTEXT_MAX_SIZE,
-					true /* is_create */);
+		ret2 = ext4_xattr_credits_for_new_inode(dir, mode, encrypt);
+		if (ret2 < 0)
+			return ERR_PTR(ret2);
+		nblocks += ret2;
 	}
 
 	ngroups = ext4_get_groups_count(sb);