linux-kernel - Re: [PATCH 1/4] vfs: add file

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Message-ID: <8737rjni6r.fsf@gamma.ozlabs.ibm.com>
Date:	Tue, 22 Mar 2016 17:24:44 +1100
From:	Daniel Axtens <dja@...ens.net>
To:	Theodore Ts'o <tytso@....edu>, Miklos Szeredi <miklos@...redi.hu>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	dhowells@...hat.com, viro@...iv.linux.org.uk,
	Goldwyn Rodrigues <rgoldwyn@...e.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	stable@...r.kernel.org
Subject: Re: [PATCH 1/4] vfs: add file_dentry()

>> From: Miklos Szeredi <mszeredi@...hat.com>
>> 
>> This series fixes bugs in nfs and ext4 due to 4bacc9c9234c ("overlayfs: Make
>> f_path always point to the overlay and f_inode to the underlay").
>> 
>> Regular files opened on overlayfs will result in the file being opened on
>> the underlying filesystem, while f_path points to the overlayfs
>> mount/dentry.
>> 
>> This confuses filesystems which get the dentry from struct file and assume
>> it's theirs.
>> 
>> Add a new helper, file_dentry() [*], to get the filesystem's own dentry
>> from the file.  This simply compares file_inode(file->f_path.dentry) to
>> file_inode(file) and if they are equal returns file->f_path.dentry (this is
>> the common, non-overlayfs case).
>> 
>> In the uncommon case (regular file on overlayfs) it will call into
>> overlayfs's ->d_native_dentry() to get the underlying dentry matching
>> file_inode(file).
>> 
>> [*] If possible, it's better simply to use file_inode() instead.

Hopefully this is not so late as to be useless!
For this entire series:
Tested-by: Daniel Axtens <dja@...ens.net>

Regards,
Daniel

>> 
>> Signed-off-by: Miklos Szeredi <mszeredi@...hat.com>
>> Tested-by: Goldwyn Rodrigues <rgoldwyn@...e.com>
>> Reviewed-by: Trond Myklebust <trond.myklebust@...marydata.com>
>> Cc: <stable@...r.kernel.org> # v4.2
>> Cc: David Howells <dhowells@...hat.com>
>> Cc: Al Viro <viro@...iv.linux.org.uk>
>> Cc: Theodore Ts'o <tytso@....edu>
>> Cc: Daniel Axtens <dja@...ens.net>
>> ---
>>  fs/open.c              | 11 +++++++++++
>>  fs/overlayfs/super.c   | 16 ++++++++++++++++
>>  include/linux/dcache.h |  1 +
>>  include/linux/fs.h     |  2 ++
>>  4 files changed, 30 insertions(+)
>
> I have this patch in the ext4.git tree, but I'd like to get an
> Acked-by from Al before I send a pull request to Linus.
>
> Al?  Any objections to my sending in this change via the ext4 tree?
>
> 						- Ted
>
>> 
>> diff --git a/fs/open.c b/fs/open.c
>> index 55bdc75e2172..6326c11eda78 100644
>> --- a/fs/open.c
>> +++ b/fs/open.c
>> @@ -831,6 +831,17 @@ char *file_path(struct file *filp, char *buf, int buflen)
>>  }
>>  EXPORT_SYMBOL(file_path);
>>  
>> +struct dentry *file_dentry(const struct file *file)
>> +{
>> +	struct dentry *dentry = file->f_path.dentry;
>> +
>> +	if (likely(d_inode(dentry) == file_inode(file)))
>> +		return dentry;
>> +	else
>> +		return dentry->d_op->d_native_dentry(dentry, file_inode(file));
>> +}
>> +EXPORT_SYMBOL(file_dentry);
>> +
>>  /**
>>   * vfs_open - open the file at the given path
>>   * @path: path to open
>> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
>> index 619ad4b016d2..5142aa2034c4 100644
>> --- a/fs/overlayfs/super.c
>> +++ b/fs/overlayfs/super.c
>> @@ -336,14 +336,30 @@ static int ovl_dentry_weak_revalidate(struct dentry *dentry, unsigned int flags)
>>  	return ret;
>>  }
>>  
>> +static struct dentry *ovl_d_native_dentry(struct dentry *dentry,
>> +					 struct inode *inode)
>> +{
>> +	struct ovl_entry *oe = dentry->d_fsdata;
>> +	struct dentry *realentry = ovl_upperdentry_dereference(oe);
>> +
>> +	if (realentry && inode == d_inode(realentry))
>> +		return realentry;
>> +	realentry = __ovl_dentry_lower(oe);
>> +	if (realentry && inode == d_inode(realentry))
>> +		return realentry;
>> +	BUG();
>> +}
>> +
>>  static const struct dentry_operations ovl_dentry_operations = {
>>  	.d_release = ovl_dentry_release,
>>  	.d_select_inode = ovl_d_select_inode,
>> +	.d_native_dentry = ovl_d_native_dentry,
>>  };
>>  
>>  static const struct dentry_operations ovl_reval_dentry_operations = {
>>  	.d_release = ovl_dentry_release,
>>  	.d_select_inode = ovl_d_select_inode,
>> +	.d_native_dentry = ovl_d_native_dentry,
>>  	.d_revalidate = ovl_dentry_revalidate,
>>  	.d_weak_revalidate = ovl_dentry_weak_revalidate,
>>  };
>> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
>> index c4b5f4b3f8f8..99ecb6de636c 100644
>> --- a/include/linux/dcache.h
>> +++ b/include/linux/dcache.h
>> @@ -161,6 +161,7 @@ struct dentry_operations {
>>  	struct vfsmount *(*d_automount)(struct path *);
>>  	int (*d_manage)(struct dentry *, bool);
>>  	struct inode *(*d_select_inode)(struct dentry *, unsigned);
>> +	struct dentry *(*d_native_dentry)(struct dentry *, struct inode *);
>>  } ____cacheline_aligned;
>>  
>>  /*
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index ae681002100a..1091d9f43271 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -1234,6 +1234,8 @@ static inline struct inode *file_inode(const struct file *f)
>>  	return f->f_inode;
>>  }
>>  
>> +extern struct dentry *file_dentry(const struct file *file);
>> +
>>  static inline int locks_lock_file_wait(struct file *filp, struct file_lock *fl)
>>  {
>>  	return locks_lock_inode_wait(file_inode(filp), fl);
>> -- 
>> 2.1.4
>>