Re: [PATCH 02/10] fs: Introduce filemap_range_has_page()
From: Andrew Morton <hidden>
Date: 2017-06-15 18:25:34
Also in:
linux-block, linux-fsdevel
On Thu, 15 Jun 2017 10:59:54 -0500 Goldwyn Rodrigues [off-list ref] wrote:
quoted hunk ↗ jump to hunk
From: Goldwyn Rodrigues <rgoldwyn-IBi9RG/b67k@public.gmane.org> 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. ...--- a/include/linux/fs.h +++ b/include/linux/fs.h@@ -2517,6 +2517,8 @@ 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 int 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 6f1be573a5e6..87aba7698584 100644 --- a/mm/filemap.c +++ b/mm/filemap.c@@ -376,6 +376,39 @@ 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 structure to wait for
"to wait for" seems wrong.
+ * @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. + */ +int filemap_range_has_page(struct address_space *mapping, + loff_t start_byte, loff_t end_byte)
Would a bool return type be better?
+{
+ pgoff_t index = start_byte >> PAGE_SHIFT;
+ pgoff_t end = end_byte >> PAGE_SHIFT;
+ struct pagevec pvec;
+ int ret;
+
+ if (end_byte < start_byte)
+ return 0;
+
+ if (mapping->nrpages == 0)
+ return 0;
+
+ pagevec_init(&pvec, 0);
+ ret = pagevec_lookup(&pvec, mapping, index, 1);
+ if (!ret)
+ return 0;
+ ret = (pvec.pages[0]->index <= end);
+ pagevec_release(&pvec);
+ return ret;
+}
+EXPORT_SYMBOL(filemap_range_has_page);
+