Re: [RFC][PATCH 1/1] ext4: Undelete Feature for Ext4

[Lubos Uhliarik <uhliarik@seznam.cz>]

Hi Andreas,

I will try to create matching patch for e2fsprogs debugfs later, after I
will finish my patch for ext4. 

You wrote, that you think inodes have their blocks zeroed out by kernel
during truncation, but in fact, it's not happening (I tested it and
there are only changes in extent header and ext4_extents structs...
Extent_indexes are untached by delete process.

Lubos

Andreas Dilger píše v Út 18. 03. 2014 v 12:23 -0600:
> On Mar 18, 2014, at 9:09 AM, Lubos Uhliarik <uhliarik@seznam.cz> wrote:
> > This patch should make undelete process for deleted files under ext4 fs easier.
> 
> Hi Lubos,
> thanks for the interesting patch.  This does seem like an improvement.
> It would be good to add more description to your commit comment, since
> it should explain what is actually being done in your patch (e.g. store
> the extent count and depth in the ext4_extent_header eh_generation field,
> ...).
> 
> It would also be good to include a matching patch for e2fsprogs debugfs
> in the "undelete" command.  I think one obstacle is the fact that inodes
> have their blocks zeroed out by the kernel during truncation.  It would
> be necessary to change the kernel slightly to avoid writing out i_blocks
> with zero if the inode is being deleted.  Otherwise, this change is not
> as useful as it could be.
> 
> Cheers, Andreas
> 
> > Signed-off-by: Lubos Uhliarik <uhliarik@seznam.cz>
> > ---
> > fs/ext4/ext4_extents.h | 14 +++++++++++
> > fs/ext4/extents.c      | 67 +++++++++++++++++++++++++++++++++++++++++++++-----
> > 2 files changed, 75 insertions(+), 6 deletions(-)
> > 
> > diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
> > index 5074fe2..22cf2cd 100644
> > --- a/fs/ext4/ext4_extents.h
> > +++ b/fs/ext4/ext4_extents.h
> > @@ -251,6 +251,20 @@ static inline void ext4_ext_store_pblock(struct ext4_extent *ex,
> > 				      0xffff);
> > }
> > 
> > +static inline void ext4_ext_store_entries(struct ext4_extent_header *eh,
> > +					  __u16 eh_entries){
> > +	eh->eh_generation &= cpu_to_le32((unsigned long) 0x0000ffff);
> > +	eh->eh_generation |= cpu_to_le32(((unsigned long) (eh_entries) << 16)
> > +				& 0xffff0000);
> > +}
> > +
> > +static inline void ext4_ext_store_depth(struct ext4_extent_header *eh,
> > +					 __u16 eh_depth){
> > +	eh->eh_generation &= cpu_to_le32((unsigned long) 0xffff0000);
> > +	eh->eh_generation |= cpu_to_le32(((unsigned long) (eh_depth))
> > +				& 0x0000ffff);
> > +}
> > +
> > /*
> >  * ext4_idx_store_pblock:
> >  * stores a large physical block number into an index struct,
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 74bc2d5..f0f3615 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -2565,6 +2565,7 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> > 	ext4_lblk_t ex_ee_block;
> > 	unsigned short ex_ee_len;
> > 	unsigned uninitialized = 0;
> > +	unsigned short ex_ee_entries;
> > 	struct ext4_extent *ex;
> > 	ext4_fsblk_t pblk;
> > 
> > @@ -2584,6 +2585,7 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> > 
> > 	ex_ee_block = le32_to_cpu(ex->ee_block);
> > 	ex_ee_len = ext4_ext_get_actual_len(ex);
> > +	ex_ee_entries = le16_to_cpu(eh->eh_entries);
> > 
> > 	trace_ext4_ext_rm_leaf(inode, start, ex, *partial_cluster);
> > 
> > @@ -2662,11 +2664,9 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> > 		if (err)
> > 			goto out;
> > 
> > -		if (num == 0)
> > -			/* this extent is removed; mark slot entirely unused */
> > -			ext4_ext_store_pblock(ex, 0);
> > +		if (num != 0)
> > +			ex->ee_len = cpu_to_le16(num);
> > 
> > -		ex->ee_len = cpu_to_le16(num);
> > 		/*
> > 		 * Do not mark uninitialized if all the blocks in the
> > 		 * extent have been removed.
> > @@ -2726,8 +2726,19 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> > 
> > 	/* if this leaf is free, then we should
> > 	 * remove it from index block above */
> > -	if (err == 0 && eh->eh_entries == 0 && path[depth].p_bh != NULL)
> > +	if (err == 0 && eh->eh_entries == 0 && path[depth].p_bh != NULL) {
> > +		err = ext4_ext_get_access(handle, inode, path + depth);
> > +		if (err)
> > +			goto out;
> > +
> > +		ext4_ext_store_entries(path[depth].p_hdr, ex_ee_entries);
> > +
> > +		err = ext4_ext_dirty(handle, inode, path + depth);
> > +		if (err)
> > +			goto out;
> > +
> > 		err = ext4_ext_rm_idx(handle, inode, path, depth);
> > +	}
> > 
> > out:
> > 	return err;
> > @@ -2760,6 +2771,7 @@ int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start,
> > 	struct super_block *sb = inode->i_sb;
> > 	int depth = ext_depth(inode);
> > 	struct ext4_ext_path *path = NULL;
> > +	unsigned short *entries_path = NULL;
> > 	long long partial_cluster = 0;
> > 	handle_t *handle;
> > 	int i = 0, err = 0;
> > @@ -2864,6 +2876,18 @@ again:
> > 	}
> > 	err = 0;
> > 
> > +	if (!inode->i_nlink) {
> > +		entries_path = kzalloc(sizeof(short) * (depth + 1),
> > +				       GFP_NOFS);
> > +		if (entries_path == NULL) {
> > +			kfree(path);
> > +			ext4_journal_stop(handle);
> > +			return -ENOMEM;
> > +		}
> > +
> > +		entries_path[0] = le16_to_cpu(ext_inode_hdr(inode)->eh_entries);
> > +	}
> > +
> > 	while (i >= 0 && err == 0) {
> > 		if (i == depth) {
> > 			/* this is leaf block */
> > @@ -2890,6 +2914,10 @@ again:
> > 			ext_debug("init index ptr: hdr 0x%p, num %d\n",
> > 				  path[i].p_hdr,
> > 				  le16_to_cpu(path[i].p_hdr->eh_entries));
> > +			if (entries_path != NULL) {
> > +				entries_path[i] = le16_to_cpu(
> > +					path[i].p_hdr->eh_entries);
> > +			}
> > 		} else {
> > 			/* we were already here, see at next index */
> > 			path[i].p_idx--;
> > @@ -2928,10 +2956,24 @@ again:
> > 		} else {
> > 			/* we finished processing this index, go up */
> > 			if (path[i].p_hdr->eh_entries == 0 && i > 0) {
> > +				if (entries_path != NULL) {
> > +					err = ext4_ext_get_access(handle,
> > +						inode, path);
> > +					if (err == 0) {
> > +						ext4_ext_store_entries(
> > +							path[i].p_hdr,
> > +							(entries_path[i]));
> > +						err = ext4_ext_dirty(handle,
> > +							inode, path);
> > +					}
> > +				}
> > +
> > 				/* index is empty, remove it;
> > 				 * handle must be already prepared by the
> > 				 * truncatei_leaf() */
> > -				err = ext4_ext_rm_idx(handle, inode, path, i);
> > +				if (err == 0)
> > +					err = ext4_ext_rm_idx(handle, inode,
> > +						path, i);
> > 			}
> > 			/* root level has p_bh == NULL, brelse() eats this */
> > 			brelse(path[i].p_bh);
> > @@ -2964,6 +3006,17 @@ again:
> > 		 */
> > 		err = ext4_ext_get_access(handle, inode, path);
> > 		if (err == 0) {
> > +			/* Store depth and entries to eh_generation to make
> > +			 * recovering deleted files easier. */
> > +			if (entries_path != NULL) {
> > +				ext4_ext_store_entries(ext_inode_hdr(inode),
> > +					(entries_path[0]));
> > +
> > +				ext4_ext_store_depth(ext_inode_hdr(inode),
> > +					le16_to_cpu(
> > +					ext_inode_hdr(inode)->eh_depth));
> > +			}
> > +
> > 			ext_inode_hdr(inode)->eh_depth = 0;
> > 			ext_inode_hdr(inode)->eh_max =
> > 				cpu_to_le16(ext4_ext_space_root(inode, 0));
> > @@ -2973,6 +3026,8 @@ again:
> > out:
> > 	ext4_ext_drop_refs(path);
> > 	kfree(path);
> > +	kfree(entries_path);
> > +
> > 	if (err == -EAGAIN) {
> > 		path = NULL;
> > 		goto again;
> > -- 
> > 1.8.3.2
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > --
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> 
> 
> Cheers, Andreas
> 
> 
> 
> 
> 


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