[Yaffs] Report 2 bugs in YAFFS for kernel

BIG 1:the "rewind code" in yaffs_readdir may cause dead loop reading
operation in NFSv3 readdir/readdirplus rpc all.
The "rewind code " in function "yaffs_readdir " is as following:

/* If the directory has changed since the open or last call to
       readdir, rewind to after the 2 canned entries. */

    if (f->f_version != inode->i_version) {
        offset = 2;
        f->f_pos = offset;
        f->f_version = inode->i_version;
    }
When  export YAFFS as the nfs server, the fd will be re-opened in  NFSv3
server callback :nfsd3_proc_readdirplus->nfsd_readdir->nfsd_open.
If the fd has been re-opened,the version of the fd recorded in
f->f_version will
be lost.The rewind code will always rewind the f->f_pos to 2, this will
replace the offset in nfs file handle.
For example,when the nfs client requests a getdents system call, and the
dirent which be read contains so many child that nfs needs to call
readdirplus rpc all more than once, after the first readdir rpc call the
offset of the fd will be passed back to server,and according to the offset,
the server calls a second readdir rpc all, the server supposes that it
reads the dirent starting at the offset.If the inode->version has been
changed during the first rpc call,the "rewind code"  will always rewind the
offset, so the error occurs.
I suggest that we may remove the "rewind code" because it is not necessary .
BUG 2:yaffs_readdir "yaffs_gross_unlock(dev)" before filldir may cause
concurrent protection problem.
 yaffs_readdir will unlock before filldir callback.The filldir callback may
calls yaffs_lookup.
yaffs_lookup has following code segment at beginning of the function:

if (current != yaffs_dev_to_lc(dev)->readdir_process)
        yaffs_gross_lock(dev);

This code is not concurrency safe.If there is more than one thread call
yaffs_readdir,the yaffs_dev_to_lc(dev)->readdir_process can be changed by
another thread after the first yaffs_readdir thread “
yaffs_gross_unlock(dev)" before filldir.

I suggest that not unlock before filldir in yaffs_readdir, also need to
change the usage of lock in yaffs_lookup.