fs: Pass a folio to page_put_link()

All callers now have a folio.  Pass it to page_put_link(), saving a
hidden call to compound_head().  Also add kernel-doc for page_get_link()
and page_put_link().

Signed-off-by: "Matthew Wilcox (Oracle)" <[email protected]>
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Christian Brauner <[email protected]>

Author: Matthew Wilcox (Oracle)

fs/fuse/dir.c

@@ -1676,7 +1676,7 @@ static const char *fuse_get_link(struct dentry *dentry, struct inode *inode,
 		goto out_err;
 	}
 
-	set_delayed_call(callback, page_put_link, &folio->page);
+	set_delayed_call(callback, page_put_link, folio);
 
 	return folio_address(folio);
 

fs/namei.c

@@ -5387,7 +5387,7 @@ static char *__page_get_link(struct dentry *dentry, struct inode *inode,
 		if (IS_ERR(folio))
 			return ERR_CAST(folio);
 	}
-	set_delayed_call(callback, page_put_link, &folio->page);
+	set_delayed_call(callback, page_put_link, folio);
 	BUG_ON(mapping_gfp_mask(mapping) & __GFP_HIGHMEM);
 	return folio_address(folio);
 }
@@ -5399,6 +5399,17 @@ const char *page_get_link_raw(struct dentry *dentry, struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(page_get_link_raw);
 
+/**
+ * page_get_link() - An implementation of the get_link inode_operation.
+ * @dentry: The directory entry which is the symlink.
+ * @inode: The inode for the symlink.
+ * @callback: Used to drop the reference to the symlink.
+ *
+ * Filesystems which store their symlinks in the page cache should use
+ * this to implement the get_link() member of their inode_operations.
+ *
+ * Return: A pointer to the NUL-terminated symlink.
+ */
 const char *page_get_link(struct dentry *dentry, struct inode *inode,
 					struct delayed_call *callback)
 {
@@ -5408,12 +5419,25 @@ const char *page_get_link(struct dentry *dentry, struct inode *inode,
 		nd_terminate_link(kaddr, inode->i_size, PAGE_SIZE - 1);
 	return kaddr;
 }
-
 EXPORT_SYMBOL(page_get_link);
 
+/**
+ * page_put_link() - Drop the reference to the symlink.
+ * @arg: The folio which contains the symlink.
+ *
+ * This is used internally by page_get_link().  It is exported for use
+ * by filesystems which need to implement a variant of page_get_link()
+ * themselves.  Despite the apparent symmetry, filesystems which use
+ * page_get_link() do not need to call page_put_link().
+ *
+ * The argument, while it has a void pointer type, must be a pointer to
+ * the folio which was retrieved from the page cache.  The delayed_call
+ * infrastructure is used to drop the reference count once the caller
+ * is done with the symlink.
+ */
 void page_put_link(void *arg)
 {
-	put_page(arg);
+	folio_put(arg);
 }
 EXPORT_SYMBOL(page_put_link);
 

fs/nfs/symlink.c

@@ -63,7 +63,7 @@ static const char *nfs_get_link(struct dentry *dentry,
 		if (IS_ERR(folio))
 			return ERR_CAST(folio);
 	}
-	set_delayed_call(done, page_put_link, &folio->page);
+	set_delayed_call(done, page_put_link, folio);
 	return folio_address(folio);
 }