xfs: split direct I/O and DAX path

So far the DAX code overloaded the direct I/O code path.  There is very little
in common between the two, and untangling them allows to clean up both variants.

As a side effect we also get separate trace points for both I/O types.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

2 files changed, 112 insertions, 29 deletions

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index dd5185dafc9f..d97e8cb99a59 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -305,13 +305,11 @@ xfs_file_dio_aio_read(
         else
                 target = ip->i_mount->m_ddev_targp;
 
-        if (!IS_DAX(inode)) {
-                /* DIO must be aligned to device logical sector size */
-                if ((iocb->ki_pos | count) & target->bt_logical_sectormask) {
-                        if (iocb->ki_pos == isize)
-                                return 0;
-                        return -EINVAL;
-                }
+        /* DIO must be aligned to device logical sector size */
+        if ((iocb->ki_pos | count) & target->bt_logical_sectormask) {
+                if (iocb->ki_pos == isize)
+                        return 0;
+                return -EINVAL;
         }
 
         /*
@@ -360,13 +358,37 @@ xfs_file_dio_aio_read(
         }
 
         data = *to;
-        if (IS_DAX(inode)) {
-                ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct,
-                                NULL, 0);
-        } else {
-                ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
-                                xfs_get_blocks_direct, NULL, NULL, 0);
+        ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
+                        xfs_get_blocks_direct, NULL, NULL, 0);
+        if (ret > 0) {
+                iocb->ki_pos += ret;
+                iov_iter_advance(to, ret);
         }
+        xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
+
+        file_accessed(iocb->ki_filp);
+        return ret;
+}
+
+STATIC ssize_t
+xfs_file_dax_read(
+        struct kiocb            *iocb,
+        struct iov_iter         *to)
+{
+        struct address_space    *mapping = iocb->ki_filp->f_mapping;
+        struct inode            *inode = mapping->host;
+        struct xfs_inode        *ip = XFS_I(inode);
+        struct iov_iter         data = *to;
+        size_t                  count = iov_iter_count(to);
+        ssize_t                 ret = 0;
+
+        trace_xfs_file_dax_read(ip, count, iocb->ki_pos);
+
+        if (!count)
+                return 0; /* skip atime */
+
+        xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
+        ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct, NULL, 0);
         if (ret > 0) {
                 iocb->ki_pos += ret;
                 iov_iter_advance(to, ret);
@@ -399,7 +421,8 @@ xfs_file_read_iter(
         struct kiocb            *iocb,
         struct iov_iter         *to)
 {
-        struct xfs_mount        *mp = XFS_I(file_inode(iocb->ki_filp))->i_mount;
+        struct inode            *inode = file_inode(iocb->ki_filp);
+        struct xfs_mount        *mp = XFS_I(inode)->i_mount;
         ssize_t                 ret = 0;
 
         XFS_STATS_INC(mp, xs_read_calls);
@@ -407,7 +430,9 @@ xfs_file_read_iter(
         if (XFS_FORCED_SHUTDOWN(mp))
                 return -EIO;
 
-        if (iocb->ki_flags & IOCB_DIRECT)
+        if (IS_DAX(inode))
+                ret = xfs_file_dax_read(iocb, to);
+        else if (iocb->ki_flags & IOCB_DIRECT)
                 ret = xfs_file_dio_aio_read(iocb, to);
         else
                 ret = xfs_file_buffered_aio_read(iocb, to);
@@ -755,8 +780,7 @@ xfs_file_dio_aio_write(
                                         mp->m_rtdev_targp : mp->m_ddev_targp;
 
         /* DIO must be aligned to device logical sector size */
-        if (!IS_DAX(inode) &&
-            ((iocb->ki_pos | count) & target->bt_logical_sectormask))
+        if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
                 return -EINVAL;
 
         /* "unaligned" here means not aligned to a filesystem block */
@@ -825,14 +849,9 @@ xfs_file_dio_aio_write(
         trace_xfs_file_direct_write(ip, count, iocb->ki_pos);
 
         data = *from;
-        if (IS_DAX(inode)) {
-                ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct,
-                                xfs_end_io_direct_write, 0);
-        } else {
-                ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
-                                xfs_get_blocks_direct, xfs_end_io_direct_write,
-                                NULL, DIO_ASYNC_EXTEND);
-        }
+        ret = __blockdev_direct_IO(iocb, inode, target->bt_bdev, &data,
+                        xfs_get_blocks_direct, xfs_end_io_direct_write,
+                        NULL, DIO_ASYNC_EXTEND);
 
         /* see generic_file_direct_write() for why this is necessary */
         if (mapping->nrpages) {
@@ -849,10 +868,70 @@ out:
         xfs_rw_iunlock(ip, iolock);
 
         /*
-         * No fallback to buffered IO on errors for XFS. DAX can result in
-         * partial writes, but direct IO will either complete fully or fail.
+         * No fallback to buffered IO on errors for XFS, direct IO will either
+         * complete fully or fail.
+         */
+        ASSERT(ret < 0 || ret == count);
+        return ret;
+}
+
+STATIC ssize_t
+xfs_file_dax_write(
+        struct kiocb            *iocb,
+        struct iov_iter         *from)
+{
+        struct address_space    *mapping = iocb->ki_filp->f_mapping;
+        struct inode            *inode = mapping->host;
+        struct xfs_inode        *ip = XFS_I(inode);
+        struct xfs_mount        *mp = ip->i_mount;
+        ssize_t                 ret = 0;
+        int                     unaligned_io = 0;
+        int                     iolock;
+        struct iov_iter         data;
+
+        /* "unaligned" here means not aligned to a filesystem block */
+        if ((iocb->ki_pos & mp->m_blockmask) ||
+            ((iocb->ki_pos + iov_iter_count(from)) & mp->m_blockmask)) {
+                unaligned_io = 1;
+                iolock = XFS_IOLOCK_EXCL;
+        } else if (mapping->nrpages) {
+                iolock = XFS_IOLOCK_EXCL;
+        } else {
+                iolock = XFS_IOLOCK_SHARED;
+        }
+        xfs_rw_ilock(ip, iolock);
+
+        ret = xfs_file_aio_write_checks(iocb, from, &iolock);
+        if (ret)
+                goto out;
+
+        /*
+         * Yes, even DAX files can have page cache attached to them:  A zeroed
+         * page is inserted into the pagecache when we have to serve a write
+         * fault on a hole.  It should never be dirtied and can simply be
+         * dropped from the pagecache once we get real data for the page.
          */
-        ASSERT(ret < 0 || ret == count || IS_DAX(VFS_I(ip)));
+        if (mapping->nrpages) {
+                ret = invalidate_inode_pages2(mapping);
+                WARN_ON_ONCE(ret);
+        }
+
+        if (iolock == XFS_IOLOCK_EXCL && !unaligned_io) {
+                xfs_rw_ilock_demote(ip, XFS_IOLOCK_EXCL);
+                iolock = XFS_IOLOCK_SHARED;
+        }
+
+        trace_xfs_file_dax_write(ip, iov_iter_count(from), iocb->ki_pos);
+
+        data = *from;
+        ret = dax_do_io(iocb, inode, &data, xfs_get_blocks_direct,
+                        xfs_end_io_direct_write, 0);
+        if (ret > 0) {
+                iocb->ki_pos += ret;
+                iov_iter_advance(from, ret);
+        }
+out:
+        xfs_rw_iunlock(ip, iolock);
         return ret;
 }
 
@@ -934,7 +1013,9 @@ xfs_file_write_iter(
         if (XFS_FORCED_SHUTDOWN(ip->i_mount))
                 return -EIO;
 
-        if ((iocb->ki_flags & IOCB_DIRECT) || IS_DAX(inode))
+        if (IS_DAX(inode))
+                ret = xfs_file_dax_write(iocb, from);
+        else if (iocb->ki_flags & IOCB_DIRECT)
                 ret = xfs_file_dio_aio_write(iocb, from);
         else
                 ret = xfs_file_buffered_aio_write(iocb, from);
diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
index a1bc5c64a573..c2876917dd89 100644
--- a/fs/xfs/xfs_trace.h
+++ b/fs/xfs/xfs_trace.h
@@ -1164,8 +1164,10 @@ DEFINE_EVENT(xfs_file_class, name,	\
         TP_ARGS(ip, count, offset))
 DEFINE_RW_EVENT(xfs_file_buffered_read);
 DEFINE_RW_EVENT(xfs_file_direct_read);
+DEFINE_RW_EVENT(xfs_file_dax_read);
 DEFINE_RW_EVENT(xfs_file_buffered_write);
 DEFINE_RW_EVENT(xfs_file_direct_write);
+DEFINE_RW_EVENT(xfs_file_dax_write);
 DEFINE_RW_EVENT(xfs_file_splice_read);
 
 DECLARE_EVENT_CLASS(xfs_page_class,