Commit 66f998f6 authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason
Browse files

fs: allow short direct-io reads to be completed via buffered IO 



This is similar to what already happens in the write case.  If we have a short
read while doing O_DIRECT, instead of just returning, fallthrough and try to
read the rest via buffered IO.  BTRFS needs this because if we encounter a
compressed or inline extent during DIO, we need to fallback on buffered.  If the
extent is compressed we need to read the entire thing into memory and
de-compress it into the users pages.  I have tested this with fsx and everything
works great.  Thanks,

Signed-off-by: default avatarJosef Bacik <josef@redhat.com>
Signed-off-by: default avatarChris Mason <chris.mason@oracle.com>
parent 3fd0a558

mm/filemap.c

+31 −5
Original line number Diff line number Diff line
@@ -1263,7 +1263,7 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov, 
{

	struct file *filp = iocb->ki_filp;

	ssize_t retval;

	unsigned long seg;

	unsigned long seg = 0;

	size_t count;

	loff_t *ppos = &iocb->ki_pos;
@@ -1290,21 +1290,47 @@ generic_file_aio_read(struct kiocb *iocb, const struct iovec *iov, 
				retval = mapping->a_ops->direct_IO(READ, iocb,

							iov, pos, nr_segs);

			}

			if (retval > 0)

			if (retval > 0) {

				*ppos = pos + retval;

			if (retval) {

				count -= retval;

			}



			/*

			 * Btrfs can have a short DIO read if we encounter

			 * compressed extents, so if there was an error, or if

			 * we've already read everything we wanted to, or if

			 * there was a short read because we hit EOF, go ahead

			 * and return.  Otherwise fallthrough to buffered io for

			 * the rest of the read.

			 */

			if (retval < 0 || !count || *ppos >= size) {

				file_accessed(filp);

				goto out;

			}

		}

	}



	count = retval;

	for (seg = 0; seg < nr_segs; seg++) {

		read_descriptor_t desc;

		loff_t offset = 0;



		/*

		 * If we did a short DIO read we need to skip the section of the

		 * iov that we've already read data into.

		 */

		if (count) {

			if (count > iov[seg].iov_len) {

				count -= iov[seg].iov_len;

				continue;

			}

			offset = count;

			count = 0;

		}



		desc.written = 0;

		desc.arg.buf = iov[seg].iov_base;

		desc.count = iov[seg].iov_len;

		desc.arg.buf = iov[seg].iov_base + offset;

		desc.count = iov[seg].iov_len - offset;

		if (desc.count == 0)

			continue;

		desc.error = 0;

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