xfs: support for synchronous DAX faults

Return IOMAP_F_DIRTY from xfs_file_iomap_begin() when asked to prepare
blocks for writing and the inode is pinned, and has dirty fields other
than the timestamps.  In __xfs_filemap_fault() we then detect this case
and call dax_finish_sync_fault() to make sure all metadata is committed,
and to insert the page table entry.

Note that this will also dirty corresponding radix tree entry which is
what we want - fsync(2) will still provide data integrity guarantees for
applications not using userspace flushing. And applications using
userspace flushing can avoid calling fsync(2) and thus avoid the
performance overhead.

[JK: Added VM_SYNC flag handling]

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 4496b45..4827e82 100644 (file)
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -44,6 +44,7 @@
 #include <linux/falloc.h>
 #include <linux/pagevec.h>
 #include <linux/backing-dev.h>
+#include <linux/mman.h>
 
 static const struct vm_operations_struct xfs_file_vm_ops;
 
@@ -1040,7 +1041,11 @@ __xfs_filemap_fault(
 
        xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED);
        if (IS_DAX(inode)) {
-               ret = dax_iomap_fault(vmf, pe_size, NULL, &xfs_iomap_ops);
+               pfn_t pfn;
+
+               ret = dax_iomap_fault(vmf, pe_size, &pfn, &xfs_iomap_ops);
+               if (ret & VM_FAULT_NEEDDSYNC)
+                       ret = dax_finish_sync_fault(vmf, pe_size, pfn);
        } else {
                if (write_fault)
                        ret = iomap_page_mkwrite(vmf, &xfs_iomap_ops);
@@ -1110,6 +1115,13 @@ xfs_file_mmap(
        struct file     *filp,
        struct vm_area_struct *vma)
 {
+       /*
+        * We don't support synchronous mappings for non-DAX files. At least
+        * until someone comes with a sensible use case.
+        */
+       if (!IS_DAX(file_inode(filp)) && (vma->vm_flags & VM_SYNC))
+               return -EOPNOTSUPP;
+
        file_accessed(filp);
        vma->vm_ops = &xfs_file_vm_ops;
        if (IS_DAX(file_inode(filp)))
@@ -1128,6 +1140,7 @@ const struct file_operations xfs_file_operations = {
        .compat_ioctl   = xfs_file_compat_ioctl,
 #endif
        .mmap           = xfs_file_mmap,
+       .mmap_supported_flags = MAP_SYNC,
        .open           = xfs_file_open,
        .release        = xfs_file_release,
        .fsync          = xfs_file_fsync,

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index f179bdf..b43be19 100644 (file)
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -33,6 +33,7 @@
 #include "xfs_error.h"
 #include "xfs_trans.h"
 #include "xfs_trans_space.h"
+#include "xfs_inode_item.h"
 #include "xfs_iomap.h"
 #include "xfs_trace.h"
 #include "xfs_icache.h"
@@ -1086,6 +1087,10 @@ xfs_file_iomap_begin(
                trace_xfs_iomap_found(ip, offset, length, 0, &imap);
        }
 
+       if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) &&
+           (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP))
+               iomap->flags |= IOMAP_F_DIRTY;
+
        xfs_bmbt_to_iomap(ip, iomap, &imap);
 
        if (shared)