David Howells <dhowells@xxxxxxxxxx> wrote:
> Would it be possible to get an IOCB_NO_READ_HOLE flag that causes a read to
> either fail entirely if there's a hole in the file or to stop at the hole,
> possibly returning -ENODATA if the hole is at the front of the file?
>
> Looking at iomap_dio_iter(), IOMAP_HOLE should be enabled in
> iomap_iter::iomap.type for this? Is it that simple?
Actually, that's not the right thing. How about the attached - at least for
direct I/O?
David
---
commit 522d2834f9994b82b1fa1f1eeeb48ede16b327c7
Author: David Howells <dhowells@xxxxxxxxxx>
Date: Fri Sep 17 11:33:41 2021 +0100
iomap: Implement IOCB_NO_READ_HOLE
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 4ecd255e0511..d2309dec27c4 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -18,6 +18,7 @@
* Private flags for iomap_dio, must not overlap with the public ones in
* iomap.h:
*/
+#define IOMAP_DIO_NO_READ_HOLE (1 << 27)
#define IOMAP_DIO_WRITE_FUA (1 << 28)
#define IOMAP_DIO_NEED_SYNC (1 << 29)
#define IOMAP_DIO_WRITE (1 << 30)
@@ -412,6 +413,8 @@ static loff_t iomap_dio_iter(const struct iomap_iter *iter,
case IOMAP_HOLE:
if (WARN_ON_ONCE(dio->flags & IOMAP_DIO_WRITE))
return -EIO;
+ if (dio->flags & IOMAP_DIO_NO_READ_HOLE)
+ return dio->size ? 0 : -ENODATA;
return iomap_dio_hole_iter(iter, dio);
case IOMAP_UNWRITTEN:
if (!(dio->flags & IOMAP_DIO_WRITE))
@@ -503,6 +506,8 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
if (iter_is_iovec(iter))
dio->flags |= IOMAP_DIO_DIRTY;
+ if (iocb->ki_flags & IOCB_NO_READ_HOLE)
+ dio->flags |= IOMAP_DIO_NO_READ_HOLE;
} else {
iomi.flags |= IOMAP_WRITE;
dio->flags |= IOMAP_DIO_WRITE;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e7a633353fd2..f4c8ca22531d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -321,6 +321,7 @@ enum rw_hint {
#define IOCB_NOIO (1 << 20)
/* can use bio alloc cache */
#define IOCB_ALLOC_CACHE (1 << 21)
+#define IOCB_NO_READ_HOLE (1 << 22) /* Don't read from a hole */
struct kiocb {
struct file *ki_filp;
