Messages in this thread | | | Date | Mon, 10 Apr 2023 13:24:15 +0800 | Subject | Re: [PATCH 4/7] erofs: introduce on-disk format for long xattr name prefixes | From | Gao Xiang <> |
| |
On 2023/4/7 22:17, Jingbo Xu wrote: > Besides the predefined xattr name prefixes, introduces long xattr name > prefixes, which work similarly as the predefined name prefixes, except > that they are user specified. > > It is especially useful for use cases together with overlayfs like > Composefs model, which introduces diverse xattr values with only a few > common xattr names (trusted.overlay.redirect, trusted.overlay.digest, > and maybe more in the future). That makes the existing predefined > prefixes ineffective in both image size and runtime performance. > > When a user specified long xattr name prefix is used, only the trailing > part of the xattr name apart from the long xattr name prefix will be > stored in erofs_xattr_entry.e_name. e_name is empty if the xattr name > matches exactly as the long xattr name prefix. All long xattr prefixes > are stored in the packed or meta inode, which depends if fragments > feature is enabled or not. > > For each long xattr name prefix, the on-disk format is kept as the same > as the unique metadata format: ALIGN({__le16 len, data}, 4), where len > represents the total size of struct erofs_xattr_long_prefix, followed > by data of struct erofs_xattr_long_prefix itself. > > Each erofs_xattr_long_prefix keeps predefined prefixes (base_index) > and the remaining prefix string without the trailing '\0'. > > Two fields are introduced to the on-disk superblock, where > xattr_prefix_count represents the total number of the long xattr name > prefixes recorded, and xattr_prefix_start represents the start offset of > recorded name prefixes in the packed/meta inode divided by 4. > > When referring to a long xattr name prefix, the highest bit (bit 7) of > erofs_xattr_entry.e_name_index is set, while the lower bits (bit 0-6) > as a whole represents the index of the referred long name prefix among > all long xattr name prefixes. > > Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Thanks, Gao Xiang
> --- > fs/erofs/erofs_fs.h | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > diff --git a/fs/erofs/erofs_fs.h b/fs/erofs/erofs_fs.h > index 44876a97cabd..ea62f83dac40 100644 > --- a/fs/erofs/erofs_fs.h > +++ b/fs/erofs/erofs_fs.h > @@ -76,7 +76,8 @@ struct erofs_super_block { > __le16 extra_devices; /* # of devices besides the primary device */ > __le16 devt_slotoff; /* startoff = devt_slotoff * devt_slotsize */ > __u8 dirblkbits; /* directory block size in bit shift */ > - __u8 reserved[5]; > + __u8 xattr_prefix_count; /* # of long xattr name prefixes */ > + __le32 xattr_prefix_start; /* start of long xattr prefixes */ > __le64 packed_nid; /* nid of the special packed inode */ > __u8 reserved2[24]; > }; > @@ -229,6 +230,13 @@ struct erofs_xattr_ibody_header { > #define EROFS_XATTR_INDEX_LUSTRE 5 > #define EROFS_XATTR_INDEX_SECURITY 6 > > +/* > + * bit 7 of e_name_index is set when it refers to a long xattr name prefix, > + * while the remained lower bits represent the index of the prefix. > + */ > +#define EROFS_XATTR_LONG_PREFIX 0x80 > +#define EROFS_XATTR_LONG_PREFIX_MASK 0x7f > + > /* xattr entry (for both inline & shared xattrs) */ > struct erofs_xattr_entry { > __u8 e_name_len; /* length of name */ > @@ -238,6 +246,12 @@ struct erofs_xattr_entry { > char e_name[]; /* attribute name */ > }; > > +/* long xattr name prefix */ > +struct erofs_xattr_long_prefix { > + __u8 base_index; /* short xattr name prefix index */ > + char infix[]; /* infix apart from short prefix */ > +}; > + > static inline unsigned int erofs_xattr_ibody_size(__le16 i_xattr_icount) > { > if (!i_xattr_icount)
| |