On Sat, May 13, 2017 at 4:25 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> On Thu, May 11, 2017 at 4:42 PM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>> This patch is based on an earlier POC by Miklos Szeredi.
>>
>> When all layers are on the same fs, and iterating a directory which
>> may contain copy up entries, call vfs_getattr() on the overlay entries
>> to make sure that d_ino will be consistent with st_ino from stat(2).
>>
> [...]
>>
>> +/*
>> + * Set d_ino for upper entries. Non-upper entries should always report
>> + * the uppermost real inode ino and should not call this function.
>> + *
>> + * When not all layer are on same fs, report real ino also for upper.
>> + *
>> + * When all layers are on the same fs, and upper has a reference to
>> + * copy up origin, call vfs_getattr() on the overlay entry to make
>> + * sure that d_ino will be consistent with st_ino from stat(2).
>> + */
>> +static int ovl_cache_update_ino(struct path *path, struct ovl_cache_entry *p)
>> +
>> +{
>> + struct dentry *dir = path->dentry;
>> + struct dentry *this = NULL;
>> + enum ovl_path_type type;
>> + u64 ino = p->real_ino;
>> + int err = 0;
>> +
>> + if (!ovl_same_sb(dir->d_sb) || WARN_ON(p->idx))
>> + goto out;
>> +
>> + if (p->name[0] == '.') {
>> + if (p->len == 1) {
>> + this = dget(dir);
>> + goto get;
>> + }
>> + if (p->len == 2 && p->name[1] == '.') {
>> + /* we shall not be moved */
>> + this = dget(dir->d_parent);
>> + goto get;
>> + }
>> + }
>> + this = lookup_one_len(p->name, dir, p->len);
>
> Mmm... that reeks of layer violation, but I can't find anything obvious
> that could go wrong from calling lookup on overlay dir here, is there?
>
> It's just so convenient to use overlay lookup here, get the overlay
> entry from cache and stat it, so I can't think of a better alternative.
>
> BTW, couldn't find anything obviously wrong with stat'ing overlay
> dir and dir->d_parent here either, is there?
One issue is permission checking: lookup needs MAY_EXEC while readdir
needs MAY_READ. So we can't just call lookup_one_len(), but will have
to do the thing by hand. Also no need to construct the overlay
dentry, just pre-loading the underlying dentries will have almost all
the pros (and cons).
Thanks,
Miklos
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