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iomap: Support partial direct I/O on user copy failures

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In iomap_dio_rw, when iomap_apply returns an -EFAULT error and the
IOMAP_DIO_PARTIAL flag is set, complete the request synchronously and
return a partial result.  This allows the caller to deal with the page
fault and retry the remainder of the request.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
This commit is contained in:
Andreas Gruenbacher 2021-07-23 01:59:41 +02:00
parent 42c498c18a
commit 97308f8b0d
2 changed files with 13 additions and 0 deletions
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6
fs/iomap/direct-io.c
View File

@ -581,6 +581,12 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
if (iov_iter_rw(iter) == READ && iomi.pos >= dio->i_size)
iov_iter_revert(iter, iomi.pos - dio->i_size);
if (ret == -EFAULT && dio->size && (dio_flags & IOMAP_DIO_PARTIAL)) {
if (!(iocb->ki_flags & IOCB_NOWAIT))
wait_for_completion = true;
ret = 0;
}
/* magic error code to fall back to buffered I/O */
if (ret == -ENOTBLK) {
wait_for_completion = true;

7
include/linux/iomap.h
View File

@ -330,6 +330,13 @@ struct iomap_dio_ops {
*/
#define IOMAP_DIO_OVERWRITE_ONLY (1 << 1)
/*
* When a page fault occurs, return a partial synchronous result and allow
* the caller to retry the rest of the operation after dealing with the page
* fault.
*/
#define IOMAP_DIO_PARTIAL (1 << 2)
ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
unsigned int dio_flags);