Re: [PATCH v2 2/2] erofs: boost negative xattr lookup with bloom filter

[Alexander Larsson]

On Wed, Jul 5, 2023 at 9:04 AM Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx> wrote:
>
> The bit value for the bloom filter map has a reverse semantics for
> compatibility.  That is, the bit value of 0 indicates existence, while
> the bit value of 1 indicates the absence of corresponding xattr.
>
> Signed-off-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
> ---
>  fs/erofs/internal.h |  2 ++
>  fs/erofs/xattr.c    | 12 ++++++++++++
>  2 files changed, 14 insertions(+)
>
> diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> index 36e32fa542f0..7e447b48a46b 100644
> --- a/fs/erofs/internal.h
> +++ b/fs/erofs/internal.h
> @@ -251,6 +251,7 @@ EROFS_FEATURE_FUNCS(fragments, incompat, INCOMPAT_FRAGMENTS)
>  EROFS_FEATURE_FUNCS(dedupe, incompat, INCOMPAT_DEDUPE)
>  EROFS_FEATURE_FUNCS(xattr_prefixes, incompat, INCOMPAT_XATTR_PREFIXES)
>  EROFS_FEATURE_FUNCS(sb_chksum, compat, COMPAT_SB_CHKSUM)
> +EROFS_FEATURE_FUNCS(xattr_filter, compat, COMPAT_XATTR_FILTER)
>
>  /* atomic flag definitions */
>  #define EROFS_I_EA_INITED_BIT  0
> @@ -270,6 +271,7 @@ struct erofs_inode {
>         unsigned char inode_isize;
>         unsigned int xattr_isize;
>
> +       unsigned long xattr_name_filter;
>         unsigned int xattr_shared_count;
>         unsigned int *xattr_shared_xattrs;
>
> diff --git a/fs/erofs/xattr.c b/fs/erofs/xattr.c
> index 40178b6e0688..1137723303d3 100644
> --- a/fs/erofs/xattr.c
> +++ b/fs/erofs/xattr.c
> @@ -5,6 +5,7 @@
>   * Copyright (C) 2021-2022, Alibaba Cloud
>   */
>  #include <linux/security.h>
> +#include <linux/xxhash.h>
>  #include "xattr.h"
>
>  struct erofs_xattr_iter {
> @@ -87,6 +88,7 @@ static int erofs_init_inode_xattrs(struct inode *inode)
>         }
>
>         ih = it.kaddr + erofs_blkoff(sb, it.pos);
> +       vi->xattr_name_filter = le32_to_cpu(ih->h_name_filter);
>         vi->xattr_shared_count = ih->h_shared_count;
>         vi->xattr_shared_xattrs = kmalloc_array(vi->xattr_shared_count,
>                                                 sizeof(uint), GFP_KERNEL);
> @@ -392,7 +394,10 @@ int erofs_getxattr(struct inode *inode, int index, const char *name,
>                    void *buffer, size_t buffer_size)
>  {
>         int ret;
> +       uint32_t bit;
>         struct erofs_xattr_iter it;
> +       struct erofs_inode *vi = EROFS_I(inode);
> +       struct erofs_sb_info *sbi = EROFS_SB(inode->i_sb);
>
>         if (!name)
>                 return -EINVAL;
> @@ -401,6 +406,13 @@ int erofs_getxattr(struct inode *inode, int index, const char *name,
>         if (ret)
>                 return ret;
>
> +       if (erofs_sb_has_xattr_filter(sbi)) {

As I said in my other mail. I would really like this to just always do
the filter check. It should be safe as older fs:es have zero in place
here, and doing this allows me to create composefs images with the
bloom filters that also work with older kernels.

> +               bit = xxh32(name, strlen(name), EROFS_XATTR_FILTER_SEED + index);
> +               bit &= EROFS_XATTR_FILTER_MASK;
> +               if (test_bit(bit, &vi->xattr_name_filter))
> +                       return -ENOATTR;
> +       }
> +
>         it.index = index;
>         it.name = (struct qstr)QSTR_INIT(name, strlen(name));
>         if (it.name.len > EROFS_NAME_LEN)
> --
> 2.19.1.6.gb485710b
>


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=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 Alexander Larsson                                Red Hat, Inc
       alexl@xxxxxxxxxx         alexander.larsson@xxxxxxxxx