[Virtio-fs] [virtiofsd PATCH v6 6/6] virtiofsd: implement persistent inode attribute based dax policy

[Jeffle Xu]

The per-file DAX feature in ext4/xfs uses the persistent inode
attribute, i.e. FS_DAX_FL/FS_XFLAG_DAX, to indicate if DAX shall be
enable for this file or not when filesystem is mounted in per-file DAX
mode.

To keep compatible with this feature in ext4/xfs, virtiofs also supports
enabling DAX depending on the persistent inode attribute, which may be
set/cleared by users inside guest or admin on host.

This policy is used when '-o dax=attr' option is specified for
virtiofsd.

Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>
---
 tools/virtiofsd/passthrough_ll.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index a5a5061906..6f75cd6d92 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -1000,7 +1000,7 @@ static int do_statx(struct lo_data *lo, int dirfd, const char *pathname,
     return 0;
 }
 
-static bool lo_should_enable_dax(struct lo_data *lo,
+static bool lo_should_enable_dax(struct lo_data *lo, struct lo_inode *inode,
                                  struct fuse_entry_param *e)
 {
     if (lo->dax == DAX_NONE || !S_ISREG(e->attr.st_mode)) {
@@ -1011,6 +1011,24 @@ static bool lo_should_enable_dax(struct lo_data *lo,
         return e->attr.st_size > FUSE_PERFILE_DAX_POINT;
     }
 
+    if (lo->dax & DAX_ATTR) {
+        int res, fd;
+        int ret = false;;
+        unsigned int attr;
+
+        fd = lo_inode_open(lo, inode, O_RDONLY);
+        if (fd == -1) {
+            return false;
+        }
+
+        res = ioctl(fd, FS_IOC_GETFLAGS, &attr);
+        if (!res && (attr & FS_DAX_FL))
+            ret = true;
+
+        close(fd);
+        return ret;
+    }
+
     return false;
 }
 
@@ -1104,7 +1122,7 @@ static int lo_do_lookup(fuse_req_t req, fuse_ino_t parent, const char *name,
     }
     e->ino = inode->fuse_ino;
 
-    if (lo_should_enable_dax(lo, e)) {
+    if (lo_should_enable_dax(lo, inode, e)) {
         e->attr_flags |= FUSE_ATTR_DAX;
     }
 
-- 
2.27.0