Merge tag 'configfs-5.13' of git://git.infradead.org/users/hch/configfs

[linux-2.6-microblaze.git] / fs / netfs / read_helper.c

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index 7256146..0b6cd3b 100644 (file)
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -1011,12 +1011,42 @@ out:
 }
 EXPORT_SYMBOL(netfs_readpage);
 
-static void netfs_clear_thp(struct page *page)
+/**
+ * netfs_skip_page_read - prep a page for writing without reading first
+ * @page: page being prepared
+ * @pos: starting position for the write
+ * @len: length of write
+ *
+ * In some cases, write_begin doesn't need to read at all:
+ * - full page write
+ * - write that lies in a page that is completely beyond EOF
+ * - write that covers the the page from start to EOF or beyond it
+ *
+ * If any of these criteria are met, then zero out the unwritten parts
+ * of the page and return true. Otherwise, return false.
+ */
+static bool netfs_skip_page_read(struct page *page, loff_t pos, size_t len)
 {
-       unsigned int i;
+       struct inode *inode = page->mapping->host;
+       loff_t i_size = i_size_read(inode);
+       size_t offset = offset_in_thp(page, pos);
+
+       /* Full page write */
+       if (offset == 0 && len >= thp_size(page))
+               return true;
+
+       /* pos beyond last page in the file */
+       if (pos - offset >= i_size)
+               goto zero_out;
+
+       /* Write that covers from the start of the page to EOF or beyond */
+       if (offset == 0 && (pos + len) >= i_size)
+               goto zero_out;
 
-       for (i = 0; i < thp_nr_pages(page); i++)
-               clear_highpage(page + i);
+       return false;
+zero_out:
+       zero_user_segments(page, 0, offset, offset + len, thp_size(page));
+       return true;
 }
 
 /**
@@ -1024,7 +1054,7 @@ static void netfs_clear_thp(struct page *page)
  * @file: The file to read from
  * @mapping: The mapping to read from
  * @pos: File position at which the write will begin
- * @len: The length of the write in this page
+ * @len: The length of the write (may extend beyond the end of the page chosen)
  * @flags: AOP_* flags
  * @_page: Where to put the resultant page
  * @_fsdata: Place for the netfs to store a cookie
@@ -1061,8 +1091,6 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
        struct inode *inode = file_inode(file);
        unsigned int debug_index = 0;
        pgoff_t index = pos >> PAGE_SHIFT;
-       int pos_in_page = pos & ~PAGE_MASK;
-       loff_t size;
        int ret;
 
        DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
@@ -1090,13 +1118,8 @@ retry:
         * within the cache granule containing the EOF, in which case we need
         * to preload the granule.
         */
-       size = i_size_read(inode);
        if (!ops->is_cache_enabled(inode) &&
-           ((pos_in_page == 0 && len == thp_size(page)) ||
-            (pos >= size) ||
-            (pos_in_page == 0 && (pos + len) >= size))) {
-               netfs_clear_thp(page);
-               SetPageUptodate(page);
+           netfs_skip_page_read(page, pos, len)) {
                netfs_stat(&netfs_n_rh_write_zskip);
                goto have_page_no_wait;
        }