[Virtio-fs] [PATCH v7 5/6] virtiofsd: implement xflag based dax policy

[Jeffle Xu]

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

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

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

Signed-off-by: Jeffle Xu <jefflexu at linux.alibaba.com>
---
 tools/virtiofsd/passthrough_ll.c | 33 ++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c
index 999c906da2..dac5063594 100644
--- a/tools/virtiofsd/passthrough_ll.c
+++ b/tools/virtiofsd/passthrough_ll.c
@@ -1026,6 +1026,35 @@ 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, struct lo_inode *inode,
+                                 struct fuse_entry_param *e)
+{
+    if (lo->dax == INODE_DAX_NONE || !S_ISREG(e->attr.st_mode)) {
+        return false;
+    }
+
+    if (lo->dax == INODE_DAX_INODE) {
+        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;
+}
+
 /*
  * Increments nlookup on the inode on success. unref_inode_lolocked() must be
  * called eventually to decrement nlookup again. If inodep is non-NULL, the
@@ -1116,6 +1145,10 @@ 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, inode, e)) {
+        e->attr_flags |= FUSE_ATTR_DAX;
+    }
+
     /* Transfer ownership of inode pointer to caller or drop it */
     if (inodep) {
         *inodep = inode;
-- 
2.27.0