> $ rpm -q kernel
> kernel-2.6.38.8-35.fc15.x86_64
>
> I am running on BTRFS filesystem.

> [pos=0, name=.]
> [pos=2, name=..]
> [pos=2, name=a]

BTRFS *IS* buggy. ".." and "a" have the same offset. Sigh.
Of course, POSIX and linux vfs require every dir entry have unique offset.

The following function in btrfs is wrong.

-----------------------------------------------------------------------------------
static int btrfs_real_readdir(struct file *filp, void *dirent,
                              filldir_t filldir)
{
 (snip)
        /* FIXME, use a real flag for deciding about the key type */
        if (root->fs_info->tree_root == root)
                key_type = BTRFS_DIR_ITEM_KEY;

        /* special case for "." */
        if (filp->f_pos == 0) {
                over = filldir(dirent, ".", 1, 1, btrfs_ino(inode), DT_DIR);
                if (over)
                        return 0;
                filp->f_pos = 1;
        }
        /* special case for .., just use the back ref */
        if (filp->f_pos == 1) {
                u64 pino = parent_ino(filp->f_path.dentry);
                over = filldir(dirent, "..", 2,
                               2, pino, DT_DIR);       /// HERE
                if (over)
                        return 0;
                filp->f_pos = 2;
        }
--------------------------------------------------------------------------------

The correct parameter is

                over = filldir(dirent, "..", 2, 1, pino, DT_DIR);


If doubt, please read procfs code.

fs/proc/base.c
----------------------------------------------------------------------------------
static int proc_readfd_common(struct file * filp, void * dirent,
                              filldir_t filldir, instantiate_t instantiate)
{
 (snip)
        switch (fd) {
                case 0:
                        if (filldir(dirent, ".", 1, 0, inode->i_ino, DT_DIR) < \
0)
                                goto out;
                        filp->f_pos++;
                case 1:
                        ino = parent_ino(dentry);
                        if (filldir(dirent, "..", 2, 1, ino, DT_DIR) < 0)
                                goto out;
                        filp->f_pos++;
----------------------------------------------------------------------------------

Thus, I'd like to switch this discussion to LKML. I'll make a patch soon.
See you again if you subscribe LKML.



> Btw I have tried the build on Koji (official Fedora build system) and this two errors did not appeared there, but unfortunately there are others.
> x86_64: http://koji.fedoraproject.org/koji/getfile?taskID=3257666&name=build.log
> i686: http://koji.fedoraproject.org/koji/getfile?taskID=3257667&name=build.log
>
> Interestingly, there appear again the bug fixed by Nobu in http://redmine.ruby-lang.org/projects/ruby-19/repository/revisions/32848

I'm sure it's unrelated.