Hi, Hu, Atom2,
> I don't have the Overlayfs code on 3.11 or 3.13. I've lookup the v11
> code in Miklos's git tree:
Fortunately I got the overlay fs code of kernel V3.18, which is mostly
same to v11 code in Miklos's git.
135 static int ovl_dir_getattr(struct vfsmount *mnt, struct dentry *dentry,
136 struct kstat *stat)
137 {
138 int err;
139 enum ovl_path_type type;
140 struct path realpath;
141
142 type = ovl_path_real(dentry, &realpath);
143 err = vfs_getattr(&realpath, stat);
144 if (err)
145 return err;
146
147 stat->dev = dentry->d_sb->s_dev;
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ here set dev number as Hu mentioned
148 stat->ino = dentry->d_inode->i_ino;
149
150 /*
151 * It's probably not worth it to count subdirs to get the
152 * correct link count. nlink=1 seems to pacify 'find' and
153 * other utilities.
154 */
155 if (type == OVL_PATH_MERGE)
156 stat->nlink = 1;
157
158 return 0;
159 }
And the d_sb->s_dev is coming from the super_block of overlayfs, which is fake.
The super block s_dev is initialized by the call trace
"mount_nodev->set_anon_super-->get_anon_bdev".
Either the dir exists in lower or exists in upper, the overlay fs fakes it exits in
overlay, which holds the fake device number.
Thanks,
George
--
George Wang 王旭
Kernel Quantity Engineer
Red Hat Software (Beijing) Co.,Ltd
IRC:xuw
Tel:+86-010-62608041
Phone:15901231579
9/F, Tower C, Raycom
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