From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Find out if the write will trigger a wait due to writeback. If yes,
return -EAGAIN.
This introduces a new function filemap_range_has_page() which
returns true if the file's mapping has a page within the range
mentioned.
Return -EINVAL for buffered AIO: there are multiple causes of
delay such as page locks, dirty throttling logic, page loading
from disk etc. which cannot be taken care of.
Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
include/linux/fs.h | 2 ++
mm/filemap.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 46 insertions(+)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bfbaba6..7e657a2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2539,6 +2539,8 @@ 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 50cee70..f8e78b3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -424,6 +424,39 @@ 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
+ * @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)
+{
+ 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);
+
static int __filemap_fdatawait_range(struct address_space *mapping,
loff_t start_byte, loff_t end_byte)
{
@@ -2543,6 +2576,17 @@ inline ssize_t generic_write_checks(struct kiocb *iocb, struct iov_iter *from)
pos = iocb->ki_pos;
+ if (iocb->ki_flags & IOCB_NONBLOCKING) {
+ loff_t end = pos + iov_iter_count(from);
+
+ if (iocb->ki_flags & IOCB_DIRECT) {
+ /* Will trigger a writeback */
+ if (filemap_range_has_page(inode->i_mapping, pos, end))
+ return -EAGAIN;
+ } else
+ return -EINVAL;
+ }
+
if (limit != RLIM_INFINITY) {
if (iocb->ki_pos >= limit) {
send_sig(SIGXFSZ, current, 0);
--
2.10.2
