参数uchar* head 是已经分配好内存的64个字节的地址
http://mysql.taobao.org/monthly/2015/08/07/
/** *先从.frm文件读取64字节 *第28和第29字节记录了key_length * *利用lseek定位到第30字节,并读取key_length长度的信息到disk_buff中 *disk_buff[0]代表了索引的个数 keys_num *disk_buff[1]代表了索引中列的个数 key_parts_num * *为了把disk_buff中的信息copy到结构体中,还要分配 keys*sizeof(KEY)+key_parts*sizeof(KEY_PARTS_INFO)大小的内存 key_buff,类型为KEY* * * *做循环 *share->key_info=key_buff; *key_part = key_buff+keys_num; * for(int i=0;i<keys;key_buff++) key_buff->key_length=xxx; xxxxx key_buf->key_part = key_part; for(j=key_buff->key_parts;j>=0;j--,key_part++) key_part->fieldnr=xxx * *share->field = field_ptr //field_ptr为新分配的内存 *share->fileds = xxx; * for(int i=0;i<xxx;field_ptr++ ) * field_ptr=xxx; * */
static int open_binary_frm(THD *thd, TABLE_SHARE *share, uchar *head,
File file)
{
;
uint new_frm_ver, field_pack_length, new_field_pack_flag;
uint interval_count, interval_parts, read_length, int_length;
uint db_create_options, keys, key_parts, n_length;
uint key_info_length, com_length, null_bit_pos;
uint extra_rec_buf_length;
uint i,j;
bool use_hash;
char *keynames, *names, *comment_pos;
uchar forminfo[];
uchar *record;
uchar *disk_buff, *strpos, *null_flags, *null_pos;
ulong pos, record_offset, *rec_per_key, rec_buff_length;
handler *handler_file= ;
KEY *keyinfo;
KEY_PART_INFO *key_part;
SQL_CRYPT *crypted=;
Field **field_ptr, *reg_field;
const char **interval_array;
enum legacy_db_type legacy_db_type;
my_bitmap_map *bitmaps;
uchar *extra_segment_buff= ;
;
uchar *format_section_fields= ;
DBUG_ENTER("open_binary_frm");
new_field_pack_flag= head[];
new_frm_ver= (head[] - FRM_VER);
field_pack_length= new_frm_ver < ? : ;
disk_buff= ;
error= ;
/* Position of the form in the form file. */
if (!(pos= get_form_pos(file, head)))
goto err; /* purecov: inspected */
mysql_file_seek(file,pos,MY_SEEK_SET,MYF());
,MYF(MY_NABP)))
goto err;
share->frm_version= head[];
share->max_rows= uint4korr(head+);
share->min_rows= uint4korr(head+);
/* Read keyinformation */
key_info_length= (uint) uint2korr(head+28);
mysql_file_seek(file, (), MY_SEEK_SET, MYF());
/** *disk_buff已经被分配了内存,大小为key_info_length */
if (read_string(file,(uchar**) &disk_buff,key_info_length))
goto err; /* purecov: inspected */
] & 0x80)
{
share->keys= keys= (disk_buff[] << ) | (disk_buff[] & 0x7f);
share->key_parts= key_parts= uint2korr(disk_buff+);
}
else
{
share->keys= keys= disk_buff[];
share->key_parts= key_parts= disk_buff[];
}
/** *因为keyinfo是MYSQL服务器这边的结构体,因此需要分配内存 */
n_length=keys*sizeof(KEY)+key_parts*sizeof(KEY_PART_INFO);
))))
goto err;
bzero((char*) keyinfo,n_length);
/** *share->key_info代表keyinfo这段内存起始地址 *keyinfo的类型为KEY*,故keyinfo++,意味着数组递增 * */
share->key_info= keyinfo;
key_part= reinterpret_cast<KEY_PART_INFO*>(keyinfo+keys);
strpos=disk_buff+;
if (!(rec_per_key= (ulong*) alloc_root(&share->mem_root,
sizeof(ulong)*key_parts)))
goto err;
; i < keys ; i++, keyinfo++)
{
keyinfo->table= ; // Updated in open_frm
)
{
keyinfo->flags= (uint) uint2korr(strpos) ^ HA_NOSAME; //索引长度,索引中列的个数
keyinfo->key_length= ();
keyinfo->key_parts= (];
keyinfo->algorithm= (];
keyinfo->block_size= uint2korr(strpos+);
strpos+=;
}
keyinfo->key_part= key_part;
keyinfo->rec_per_key= rec_per_key;
for (j=keyinfo->key_parts ; j-- ; key_part++)
{
*rec_per_key++=;
key_part->fieldnr= (uint16) (uint2korr(strpos) & FIELD_NR_MASK);
key_part->offset= ()-;
key_part->key_type= ();
}
}
keynames=(char*) key_part;
strpos+= (strmov(keynames, (;
//reading index comments
; i < keys; i++, keyinfo++)
{
if (keyinfo->flags & HA_USES_COMMENT)
{
keyinfo->comment.length= uint2korr(strpos);
keyinfo->comment.str= strmake_root(&share->mem_root, (,
keyinfo->comment.length);
strpos+= + keyinfo->comment.length;
}
}
share->key_block_size= uint2korr(head+);
share->fields= uint2korr(forminfo+);
pos= uint2korr(forminfo+); /* Length of all screens */
n_length= uint2korr(forminfo+);
share->null_fields= uint2korr(forminfo+);
com_length= uint2korr(forminfo+);
if (!(field_ptr = (Field **)
alloc_root(&share->mem_root,
()*sizeof(Field*)+
interval_count*sizeof(TYPELIB)+
(share->fields+interval_parts+
keys+)*sizeof(char *)+
(n_length+int_length+com_length)))))
goto err; /* purecov: inspected */
/** *field_ptr也是刚分配内存的起始地址,赋值给share->field */
share->field= field_ptr;
read_length=(uint) (share->fields * field_pack_length +
pos+ (uint) (n_length+int_length+com_length));
if (read_string(file,(uchar**) &disk_buff,read_length))
goto err; /* purecov: inspected */
strpos= disk_buff+pos;
if (keynames)
fix_type_pointers(&interval_array, &share->keynames, , &keynames);
/* Allocate handler */
if (!(handler_file= get_new_handler(share, thd->mem_root,
share->db_type())))
goto err;
record= share->default_values-; /* Fieldstart = 1 */
if (share->null_field_first)
{
null_flags= null_pos= (uchar*) record+;
null_bit_pos= (db_create_options & HA_OPTION_PACK_RECORD) ? : ;
/*
null_bytes below is only correct under the condition that
there are no bit fields. Correct values is set below after the
table struct is initialized
*/
share->null_bytes= (share->null_fields + null_bit_pos + ) / ;
}
; i < share->fields; i++, strpos+=field_pack_length, field_ptr++)
{
uint pack_flag, interval_nr, unireg_type, recpos, field_length;
enum_field_types field_type;
CHARSET_INFO *charset=NULL;
Field::geometry_type geom_type= Field::GEOM_GEOMETRY;
LEX_STRING comment;
)
{
/* new frm file in 4.1 */
field_length= uint2korr(strpos+);
recpos= uint3korr(strpos+);
pack_flag= uint2korr(strpos+);
unireg_type= (];
interval_nr= (];
);
field_type=(enum_field_types) (];
}
/** *这里的field_ptr其实是个FIELD*的对象 */
*field_ptr= reg_field=
make_field(share, record+recpos,
(uint32) field_length,
null_pos, null_bit_pos,
pack_flag,
field_type,
charset,
geom_type,
(Field::utype) MTYP_TYPENR(unireg_type),
(interval_nr ?
share->intervals+interval_nr- :
(TYPELIB*) ),
share->fieldnames.type_names[i]);
}//循环结束
*field_ptr=; // End marker
/* Fix key->name and key_part->field */
if (key_parts)
{
uint primary_key=(uint) (find_type(primary_key_name, &share->keynames,
FIND_TYPE_NO_PREFIX) - );
longlong ha_option= handler_file->ha_table_flags();
keyinfo= share->key_info;
key_part= keyinfo->key_part;
/** *share->keys本身是个结构体数组, *里面每一个key,设置其name, *key中的key_part也是个结构体数组,其中的filednr为share->filed该数组中的下标 * */
; key < share->keys ; key++,keyinfo++)
{
;
keyinfo->name=(char*) share->keynames.type_names[key];
; i < keyinfo->key_parts ; key_part++,i++)
{
Field *field;
key_part->fieldnr= (uint16) find_field(share->field,share->default_values,(uint) key_part->offset,(uint) key_part->length);
field= key_part->field= share->field[key_part->fieldnr-];
key_part->type= field->key_type();
if (field->null_ptr)
{
key_part->null_offset=(uint) ((uchar*) field->null_ptr -
share->default_values);
key_part->null_bit= field->null_bit;
key_part->store_length+=HA_KEY_NULL_LENGTH;
keyinfo->flags|=HA_NULL_PART_KEY;
keyinfo->extra_length+= HA_KEY_NULL_LENGTH;
keyinfo->key_length+= HA_KEY_NULL_LENGTH;
}
}
share->total_key_length+= keyinfo->key_length;
}
}
/*
the correct null_bytes can now be set, since bitfields have been taken
into account
*/
share->null_bytes= (null_pos - (uchar*) null_flags +
(null_bit_pos + ) / );
share->last_null_bit_pos= null_bit_pos;
share->db_low_byte_first= handler_file->low_byte_first();
share->column_bitmap_size= bitmap_buffer_size(share->fields);
if (!(bitmaps= (my_bitmap_map*) alloc_root(&share->mem_root,
share->column_bitmap_size)))
goto err;
bitmap_init(&share->all_set, bitmaps, share->fields, FALSE);
bitmap_set_all(&share->all_set);
delete handler_file;
my_free(extra_segment_buff);
DBUG_RETURN ();
err:
share->error= error;
share->open_errno= my_errno;
share->errarg= errarg;
my_free(disk_buff);
my_free(extra_segment_buff);
delete crypted;
delete handler_file;
my_hash_free(&share->name_hash);
if (share->ha_data_destroy)
{
share->ha_data_destroy(share->ha_data);
share->ha_data_destroy= NULL;
}
#ifdef WITH_PARTITION_STORAGE_ENGINE
if (share->ha_part_data_destroy)
{
share->ha_part_data_destroy(share->ha_part_data);
share->ha_data_destroy= NULL;
}
#endif /* WITH_PARTITION_STORAGE_ENGINE */
open_table_error(share, error, share->open_errno, errarg);
DBUG_RETURN(error);
} /* open_binary_frm */