erofs: boost negative xattr lookup with bloom filter

Optimise the negative xattr lookup with bloom filter.

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.

The initial version is _only_ enabled when xattr_filter_reserved is
zero.  The filter map internals may change in the future, in which case
the reserved flag will be set non-zero and we don't need bothering the
compatible bits again at that time.  For now disable the optimization if
this reserved flag is non-zero.
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230722094538.11754-3-jefflexu@linux.alibaba.comSigned-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/Kconfig

@@ -38,6 +38,7 @@ config EROFS_FS_DEBUG
 config EROFS_FS_XATTR
 	bool "EROFS extended attributes"
 	depends on EROFS_FS
+	select XXHASH
 	default y
 	help
 	  Extended attributes are name:value pairs associated with inodes by

fs/erofs/internal.h

@@ -151,6 +151,7 @@ struct erofs_sb_info {
 	u32 xattr_prefix_start;
 	u8 xattr_prefix_count;
 	struct erofs_xattr_prefix_item *xattr_prefixes;
+	unsigned int xattr_filter_reserved;
 #endif
 	u16 device_id_mask;	/* valid bits of device id to be used */
 
@@ -251,6 +252,7 @@ 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 +272,7 @@ struct erofs_inode {
 	unsigned char inode_isize;
 	unsigned int xattr_isize;
 
+	unsigned int xattr_name_filter;
 	unsigned int xattr_shared_count;
 	unsigned int *xattr_shared_xattrs;
 

fs/erofs/super.c

@@ -391,6 +391,7 @@ static int erofs_read_superblock(struct super_block *sb)
 	sbi->xattr_blkaddr = le32_to_cpu(dsb->xattr_blkaddr);
 	sbi->xattr_prefix_start = le32_to_cpu(dsb->xattr_prefix_start);
 	sbi->xattr_prefix_count = dsb->xattr_prefix_count;
+	sbi->xattr_filter_reserved = dsb->xattr_filter_reserved;
 #endif
 	sbi->islotbits = ilog2(sizeof(struct erofs_inode_compact));
 	sbi->root_nid = le16_to_cpu(dsb->root_nid);

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;
+	unsigned int hashbit;
 	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 +406,15 @@ int erofs_getxattr(struct inode *inode, int index, const char *name,
 	if (ret)
 		return ret;
 
+	/* reserved flag is non-zero if there's any change of on-disk format */
+	if (erofs_sb_has_xattr_filter(sbi) && !sbi->xattr_filter_reserved) {
+		hashbit = xxh32(name, strlen(name),
+				EROFS_XATTR_FILTER_SEED + index);
+		hashbit &= EROFS_XATTR_FILTER_BITS - 1;
+		if (vi->xattr_name_filter & (1U << hashbit))
+			return -ENOATTR;
+	}
+
 	it.index = index;
 	it.name = (struct qstr)QSTR_INIT(name, strlen(name));
 	if (it.name.len > EROFS_NAME_LEN)