linux-kernel - Re: [PATCH] ext4: Support fast symlinks from ext3 file systems

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Message-Id: <24E86306-4A6C-48AE-9999-A9D935A2DC12@dilger.ca>
Date:   Mon, 27 Nov 2017 11:08:53 -0700
From:   Andreas Dilger <adilger@...ger.ca>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     tytso@....edu, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] ext4: Support fast symlinks from ext3 file systems

On Nov 27, 2017, at 10:37 AM, Andi Kleen <andi@...stfloor.org> wrote:
> 
> From: Andi Kleen <ak@...ux.intel.com>
> 
> dbb3c27f5b91c4 (ext4: change fast symlink test to not rely on i_blocks)
> broke ~10 years old ext3 file systems created by 2.6.17. Any ELF
> executable fails because the /lib/ld-linux.so.2 fast symlink
> cannot be read anymore.
> 
> The patch assumed fast symlinks were created in a specific way,
> but that's not true on these really old file systems.
> 
> The new behavior is apparently needed only with the large EA inode
> feature.
> 
> Revert to the old behavior if the large EA inode feature is not set.
> 
> This makes my old VM boot again.
> 
> Fixes: dbb3c27f5b91c4 (ext4: change fast symlink test to not rely ...)
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>

Reviewed-by: Andreas Dilger <adilger@...ger.ca>

> ---
> fs/ext4/inode.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0992d76f7ab1..6b82b0ff5e0b 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -149,6 +149,15 @@ static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
>  */
> int ext4_inode_is_fast_symlink(struct inode *inode)
> {
> +	if (!(EXT4_I(inode)->i_flags & EXT4_EA_INODE_FL)) {
> +		int ea_blocks = EXT4_I(inode)->i_file_acl ?
> +				EXT4_CLUSTER_SIZE(inode->i_sb) >> 9 : 0;
> +
> +		if (ext4_has_inline_data(inode))
> +			return 0;
> +
> +		return (S_ISLNK(inode->i_mode) && inode->i_blocks - ea_blocks == 0);
> +	}
> 	return S_ISLNK(inode->i_mode) && inode->i_size &&
> 	       (inode->i_size < EXT4_N_BLOCKS * 4);
> }
> --
> 2.13.6
> 


Cheers, Andreas






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