virtiofsd: Reset O_DIRECT flag during file open

If an application wants to do direct IO and opens a file with O_DIRECT
in guest, that does not necessarily mean that we need to bypass page
cache on host as well. So reset this flag on host.

If somebody needs to bypass page cache on host as well (and it is safe to
do so), we can add a knob in daemon later to control this behavior.

I check virtio-9p and they do reset O_DIRECT flag.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

tools/virtiofsd/passthrough_ll.c

@@ -1721,6 +1721,13 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,
         goto out;
     }
 
+    /*
+     * O_DIRECT in guest should not necessarily mean bypassing page
+     * cache on host as well. If somebody needs that behavior, it
+     * probably should be a configuration knob in daemon.
+     */
+    fi->flags &= ~O_DIRECT;
+
     fd = openat(parent_inode->fd, name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,
                 mode);
     err = fd == -1 ? errno : 0;
@@ -1950,6 +1957,13 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)
         fi->flags &= ~O_APPEND;
     }
 
+    /*
+     * O_DIRECT in guest should not necessarily mean bypassing page
+     * cache on host as well. If somebody needs that behavior, it
+     * probably should be a configuration knob in daemon.
+     */
+    fi->flags &= ~O_DIRECT;
+
     sprintf(buf, "%i", lo_fd(req, ino));
     fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW);
     if (fd == -1) {