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[PATCH 5/8] xfs: add DAX file operations support

To: xfs@xxxxxxxxxxx
Subject: [PATCH 5/8] xfs: add DAX file operations support
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Tue, 24 Mar 2015 21:51:03 +1100
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, willy@xxxxxxxxxxxxxxx, jack@xxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1427194266-2885-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1427194266-2885-1-git-send-email-david@xxxxxxxxxxxxx>
From: Dave Chinner <dchinner@xxxxxxxxxx>

Add the initial support for DAX file operations to XFS. This
includes the necessary block allocation and mmap page fault hooks
for DAX to function.

Note: we specifically have to disable splice_read/write from
occurring because they are dependent on usingthe page cache for
correct operation. We have no page cache for DAX, so we need to
disable them completely on DAX inodes.

Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
 fs/xfs/xfs_aops.c |  73 ++++++++++++++++++++++++++++++++--
 fs/xfs/xfs_aops.h |   7 +++-
 fs/xfs/xfs_file.c | 116 ++++++++++++++++++++++++++++++++----------------------
 3 files changed, 143 insertions(+), 53 deletions(-)

diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 3a9b7a1..3fc5052 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1233,13 +1233,64 @@ xfs_vm_releasepage(
        return try_to_free_buffers(page);
 }
 
+/*
+ * For DAX we need a mapping buffer callback for unwritten extent conversion
+ * when page faults allocation blocks and then zero them.
+ */
+#ifdef CONFIG_FS_DAX
+static struct xfs_ioend *
+xfs_dax_alloc_ioend(
+       struct inode    *inode,
+       xfs_off_t       offset,
+       ssize_t         size)
+{
+       struct xfs_ioend *ioend;
+
+       ASSERT(IS_DAX(inode));
+       ioend = xfs_alloc_ioend(inode, XFS_IO_UNWRITTEN);
+       ioend->io_offset = offset;
+       ioend->io_size = size;
+       return ioend;
+}
+
+void
+xfs_get_blocks_dax_complete(
+       struct buffer_head      *bh,
+       int                     uptodate)
+{
+       struct xfs_ioend        *ioend = bh->b_private;
+       struct xfs_inode        *ip = XFS_I(ioend->io_inode);
+       int                     error;
+
+       ASSERT(IS_DAX(ioend->io_inode));
+
+       /* if there was an error zeroing, then don't convert it */
+       if (!uptodate)
+               goto out_free;
+
+       error = xfs_iomap_write_unwritten(ip, ioend->io_offset, ioend->io_size);
+       if (error)
+               xfs_warn(ip->i_mount,
+"%s: conversion failed, ino 0x%llx, offset 0x%llx, len 0x%lx, error %d\n",
+                       __func__, ip->i_ino, ioend->io_offset,
+                       ioend->io_size, error);
+out_free:
+       mempool_free(ioend, xfs_ioend_pool);
+
+}
+#else
+#define xfs_dax_alloc_ioend(i,o,s)     NULL
+void xfs_get_blocks_dax_complete(struct buffer_head *bh, int uptodate) { }
+#endif
+
 STATIC int
 __xfs_get_blocks(
        struct inode            *inode,
        sector_t                iblock,
        struct buffer_head      *bh_result,
        int                     create,
-       int                     direct)
+       bool                    direct,
+       bool                    clear)
 {
        struct xfs_inode        *ip = XFS_I(inode);
        struct xfs_mount        *mp = ip->i_mount;
@@ -1304,6 +1355,7 @@ __xfs_get_blocks(
                        if (error)
                                return error;
                        new = 1;
+
                } else {
                        /*
                         * Delalloc reservations do not require a transaction,
@@ -1340,7 +1392,10 @@ __xfs_get_blocks(
                if (create || !ISUNWRITTEN(&imap))
                        xfs_map_buffer(inode, bh_result, &imap, offset);
                if (create && ISUNWRITTEN(&imap)) {
-                       if (direct) {
+                       if (clear) {
+                               bh_result->b_private = xfs_dax_alloc_ioend(
+                                                       inode, offset, size);
+                       } else if (direct) {
                                bh_result->b_private = inode;
                                set_buffer_defer_completion(bh_result);
                        }
@@ -1425,7 +1480,7 @@ xfs_get_blocks(
        struct buffer_head      *bh_result,
        int                     create)
 {
-       return __xfs_get_blocks(inode, iblock, bh_result, create, 0);
+       return __xfs_get_blocks(inode, iblock, bh_result, create, false, false);
 }
 
 STATIC int
@@ -1435,7 +1490,17 @@ xfs_get_blocks_direct(
        struct buffer_head      *bh_result,
        int                     create)
 {
-       return __xfs_get_blocks(inode, iblock, bh_result, create, 1);
+       return __xfs_get_blocks(inode, iblock, bh_result, create, true, false);
+}
+
+int
+xfs_get_blocks_dax(
+       struct inode            *inode,
+       sector_t                iblock,
+       struct buffer_head      *bh_result,
+       int                     create)
+{
+       return __xfs_get_blocks(inode, iblock, bh_result, create, true, true);
 }
 
 /*
diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h
index ac644e0..7c6fb3f 100644
--- a/fs/xfs/xfs_aops.h
+++ b/fs/xfs/xfs_aops.h
@@ -53,7 +53,12 @@ typedef struct xfs_ioend {
 } xfs_ioend_t;
 
 extern const struct address_space_operations xfs_address_space_operations;
-extern int xfs_get_blocks(struct inode *, sector_t, struct buffer_head *, int);
+
+int    xfs_get_blocks(struct inode *inode, sector_t offset,
+                      struct buffer_head *map_bh, int create);
+int    xfs_get_blocks_dax(struct inode *inode, sector_t offset,
+                          struct buffer_head *map_bh, int create);
+void   xfs_get_blocks_dax_complete(struct buffer_head *bh, int uptodate);
 
 extern void xfs_count_page_state(struct page *, int *, int *);
 
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 94713c2..8017175 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -385,7 +385,11 @@ xfs_file_splice_read(
 
        trace_xfs_file_splice_read(ip, count, *ppos, ioflags);
 
-       ret = generic_file_splice_read(infilp, ppos, pipe, count, flags);
+       /* for dax, we need to avoid the page cache */
+       if (IS_DAX(VFS_I(ip)))
+               ret = default_file_splice_read(infilp, ppos, pipe, count, 
flags);
+       else
+               ret = generic_file_splice_read(infilp, ppos, pipe, count, 
flags);
        if (ret > 0)
                XFS_STATS_ADD(xs_read_bytes, ret);
 
@@ -654,7 +658,7 @@ xfs_file_dio_aio_write(
                                        mp->m_rtdev_targp : mp->m_ddev_targp;
 
        /* DIO must be aligned to device logical sector size */
-       if ((pos | count) & target->bt_logical_sectormask)
+       if (!IS_DAX(inode) && (pos | count) & target->bt_logical_sectormask)
                return -EINVAL;
 
        /* "unaligned" here means not aligned to a filesystem block */
@@ -724,8 +728,11 @@ xfs_file_dio_aio_write(
 out:
        xfs_rw_iunlock(ip, iolock);
 
-       /* No fallback to buffered IO on errors for XFS. */
-       ASSERT(ret < 0 || ret == count);
+       /*
+        * No fallback to buffered IO on errors for XFS. DAX can result in
+        * partial writes, but direct IO will either complete fully or fail.
+        */
+       ASSERT(ret < 0 || ret == count || IS_DAX(VFS_I(ip)));
        return ret;
 }
 
@@ -810,7 +817,7 @@ xfs_file_write_iter(
        if (XFS_FORCED_SHUTDOWN(ip->i_mount))
                return -EIO;
 
-       if (unlikely(file->f_flags & O_DIRECT))
+       if ((file->f_flags & O_DIRECT) || IS_DAX(inode))
                ret = xfs_file_dio_aio_write(iocb, from);
        else
                ret = xfs_file_buffered_aio_write(iocb, from);
@@ -1031,17 +1038,6 @@ xfs_file_readdir(
        return xfs_readdir(ip, ctx, bufsize);
 }
 
-STATIC int
-xfs_file_mmap(
-       struct file     *filp,
-       struct vm_area_struct *vma)
-{
-       vma->vm_ops = &xfs_file_vm_ops;
-
-       file_accessed(filp);
-       return 0;
-}
-
 /*
  * This type is designed to indicate the type of offset we would like
  * to search from page cache for xfs_seek_hole_data().
@@ -1422,26 +1418,11 @@ xfs_file_llseek(
  * ordering of:
  *
  * mmap_sem (MM)
- *   i_mmap_lock (XFS - truncate serialisation)
- *     page_lock (MM)
- *       i_lock (XFS - extent map serialisation)
+ *   sb_start_pagefault(vfs, freeze)
+ *     i_mmap_lock (XFS - truncate serialisation)
+ *       page_lock (MM)
+ *         i_lock (XFS - extent map serialisation)
  */
-STATIC int
-xfs_filemap_fault(
-       struct vm_area_struct   *vma,
-       struct vm_fault         *vmf)
-{
-       struct xfs_inode        *ip = XFS_I(vma->vm_file->f_mapping->host);
-       int                     error;
-
-       trace_xfs_filemap_fault(ip);
-
-       xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
-       error = filemap_fault(vma, vmf);
-       xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
-
-       return error;
-}
 
 /*
  * mmap()d file has taken write protection fault and is being made writable. We
@@ -1454,21 +1435,66 @@ xfs_filemap_page_mkwrite(
        struct vm_area_struct   *vma,
        struct vm_fault         *vmf)
 {
-       struct xfs_inode        *ip = XFS_I(vma->vm_file->f_mapping->host);
+       struct inode            *inode = file_inode(vma->vm_file);
        int                     ret;
 
-       trace_xfs_filemap_page_mkwrite(ip);
+       trace_xfs_filemap_page_mkwrite(XFS_I(inode));
 
-       sb_start_pagefault(VFS_I(ip)->i_sb);
+       sb_start_pagefault(inode->i_sb);
        file_update_time(vma->vm_file);
-       xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
+       xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
+
+       if (IS_DAX(inode)) {
+               ret = __dax_mkwrite(vma, vmf, xfs_get_blocks_dax,
+                                   xfs_get_blocks_dax_complete);
+       } else {
+               ret = __block_page_mkwrite(vma, vmf, xfs_get_blocks);
+               ret = block_page_mkwrite_return(ret);
+       }
+
+       xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
+       sb_end_pagefault(inode->i_sb);
+
+       return ret;
+}
+
+STATIC int
+xfs_filemap_fault(
+       struct vm_area_struct   *vma,
+       struct vm_fault         *vmf)
+{
+       struct xfs_inode        *ip = XFS_I(file_inode(vma->vm_file));
+       int                     ret;
 
-       ret = __block_page_mkwrite(vma, vmf, xfs_get_blocks);
+       trace_xfs_filemap_fault(ip);
+
+       /* DAX can shortcut the normal fault path on write faults! */
+       if ((vmf->flags & FAULT_FLAG_WRITE) && IS_DAX(VFS_I(ip)))
+               return xfs_filemap_page_mkwrite(vma, vmf);
 
+       xfs_ilock(ip, XFS_MMAPLOCK_SHARED);
+       ret = filemap_fault(vma, vmf);
        xfs_iunlock(ip, XFS_MMAPLOCK_SHARED);
-       sb_end_pagefault(VFS_I(ip)->i_sb);
 
-       return block_page_mkwrite_return(ret);
+       return ret;
+}
+
+static const struct vm_operations_struct xfs_file_vm_ops = {
+       .fault          = xfs_filemap_fault,
+       .map_pages      = filemap_map_pages,
+       .page_mkwrite   = xfs_filemap_page_mkwrite,
+};
+
+STATIC int
+xfs_file_mmap(
+       struct file     *filp,
+       struct vm_area_struct *vma)
+{
+       file_accessed(filp);
+       vma->vm_ops = &xfs_file_vm_ops;
+       if (IS_DAX(file_inode(filp)))
+               vma->vm_flags |= VM_MIXEDMAP;
+       return 0;
 }
 
 const struct file_operations xfs_file_operations = {
@@ -1501,9 +1527,3 @@ const struct file_operations xfs_dir_file_operations = {
 #endif
        .fsync          = xfs_dir_fsync,
 };
-
-static const struct vm_operations_struct xfs_file_vm_ops = {
-       .fault          = xfs_filemap_fault,
-       .map_pages      = filemap_map_pages,
-       .page_mkwrite   = xfs_filemap_page_mkwrite,
-};
-- 
2.0.0

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