fs: Introduce filemap_range_has_page()

filemap_range_has_page() return true if the file's mapping has
a page within the range mentioned. This function will be used
to check if a write() call will cause a writeback of previous
writes.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 96a1a1fa54a944b7a108c94fbc234deb6878b28a..0d34f5b5a6b065ab38c6bf1dd4176dfa1d3e18d7 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2518,6 +2518,8 @@ extern int filemap_fdatawait(struct address_space *);
 extern void filemap_fdatawait_keep_errors(struct address_space *);
 extern int filemap_fdatawait_range(struct address_space *, loff_t lstart,
                                   loff_t lend);
+extern bool filemap_range_has_page(struct address_space *, loff_t lstart,
+                                 loff_t lend);
 extern int filemap_write_and_wait(struct address_space *mapping);
 extern int filemap_write_and_wait_range(struct address_space *mapping,
                                        loff_t lstart, loff_t lend);

diff --git a/mm/filemap.c b/mm/filemap.c
index 6f1be573a5e60fbb0c4a6cbcf85df9b32b0fc673..9b39a2390b9e40169c2af7019f59953c4ddecee5 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -376,6 +376,38 @@ int filemap_flush(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_flush);
 
+/**
+ * filemap_range_has_page - check if a page exists in range.
+ * @mapping:           address space within which to check
+ * @start_byte:        offset in bytes where the range starts
+ * @end_byte:          offset in bytes where the range ends (inclusive)
+ *
+ * Find at least one page in the range supplied, usually used to check if
+ * direct writing in this range will trigger a writeback.
+ */
+bool filemap_range_has_page(struct address_space *mapping,
+                          loff_t start_byte, loff_t end_byte)
+{
+       pgoff_t index = start_byte >> PAGE_SHIFT;
+       pgoff_t end = end_byte >> PAGE_SHIFT;
+       struct pagevec pvec;
+       bool ret;
+
+       if (end_byte < start_byte)
+               return false;
+
+       if (mapping->nrpages == 0)
+               return false;
+
+       pagevec_init(&pvec, 0);
+       if (!pagevec_lookup(&pvec, mapping, index, 1))
+               return false;
+       ret = (pvec.pages[0]->index <= end);
+       pagevec_release(&pvec);
+       return ret;
+}
+EXPORT_SYMBOL(filemap_range_has_page);
+
 static int __filemap_fdatawait_range(struct address_space *mapping,
                                     loff_t start_byte, loff_t end_byte)
 {