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/**
 * extlinux.c
 *
 *
 */
#include "ext2_fs.h"
#include "cache.h"
#include "types.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/* 
 * File structure, This holds the information for each currently open file 
 */
struct open_file_t {
        __u32 file_bytesleft;  /* Number of bytes left ( 0 = free ) */
        __u32 file_sector;     /* Next linear sector to read */
        __u32 file_in_sec;     /* Sector where inode lives */
        __u16 file_in_off;
        __u16 file_mode;
};

/*
  struct getc_file {
  __u16 gc_file;
  __u16 gc_bufbytes;
  __u16 gc_bufdata; 
  __u8  gc_unget_cnt;
  __u8  gc_unget_buf[9];  
  };
*/
struct getc_file {
        struct open_file_t * gc_file;             /* file pointer */
        __u16 gc_bufbytes;         /* Bytes left in buffer */
        __u16 gc_bufdata;          /* pointer to data in buffer */
        __u8  gc_unget_cnt;        /* Character pushed back count */
        __u8  gc_unget_buf[7];     /* Character pushed back buffer */
};




#define FILENAME_MAX_LG2 8
#define FILENAME_MAX_    ( 1 << FILENAME_MAX_LG2 )

#define LDLINUX_MAGIC    0x3eb202fex

#define MAX_OPEN_LG2     6
#define MAX_OPEN         ( 1 << MAX_OPEN_LG2 )

#define SECTOR_SHIFT     9
#define SECTOR_SIZE      ( 1 << SECTOR_SHIFT )


#define MAX_SYMLINKS     64
#define SYMLINK_SECTORS  2

#define ROOT_DIR_WORD    0x002F
#define CUR_DIR_DWORD    0x0000002F2E




#define MAX_GETC_LG2       4
#define MAX_GETC           ( 1 << MAX_GETC_LG2 )
#define bytes_per_getc_lg2 ( 16 - MAX_GETC_LG2 )
#define bytes_per_getc     ( 1 << bytes_per_getc_lg2 )
#define secs_per_getc      ( bytes_per_getc / SECTOR_SIZE )
#define MAX_UNGET          7

#define getc_file_lg2       4
#define getc_file_size     ( 1 << getc_file_lg2 )

char GetCStack[getc_file_size * MAX_GETC] = {0,};
__u32 CurrentGetC = (__u32) &GetCStack[getc_file_size * MAX_GETC];



struct ext2_super_block sb;

struct ext2_inode ThisInode;
struct open_file_t Files[MAX_OPEN];


__u32 ClustBytesShift, ClustSize, ClustShift;
__u32 SecPerClust, ClustMask;
__u32 PtrsPerBlock1, PtrsPerBlock2, PtrsPerBlock3;
__u32 DescPerBlock, InodePerBlock;

/* a static value, which is the boot/extlinux's inode number */
__u32 CurrentDir = 13;

/* for EXTLINUX, we make blk_size be the size of a block */
int blk_size;


#define TRACKBUFSIZE 8192
char  trackbuf[TRACKBUFSIZE];
__u32 EndBlock;


char SymlinkBuf[SYMLINK_SECTORS * SECTOR_SIZE + 64];
char *SymlinkTmpBuf = trackbuf;
char *lnk_end;
char *SymlinkTmpBufEnd = trackbuf + SYMLINK_SECTORS * SECTOR_SIZE+64;


/**
 * strecpy:
 *
 * just like the function strcpy(), except it returns non-zero if overflow.
 *
 * well, in Syslinux, strcpy() will advance both the dst and src string pointer.
 * 
 */
int strecpy(char *dst, char *src, char *end)
{
        while ( *src != '\0' )
                *dst++ = *src++;
        *dst = '\0';
       
        if ( dst > end )
                return 1;
        else 
                return 0;
}



/**
 * allocate_file:
 * 
 * Allocate a file structure
 *
 * @return: if successful return the file pointer, or return NULL
 *
 */
struct open_file_t *allocate_file()
{
        struct open_file_t *file;
        int i = 0;
        
        file = Files;

        for (; i < MAX_OPEN; i ++ ) {
                if ( file->file_bytesleft == 0 ) /* found it */
                        return file;
                file ++;
        }

        return NULL; /* not found */
}


/**
 * getlinsec_ext:
 *
 * same as getlinsec, except load any sector from the zero
 * block as all zeros; use to load any data derived from
 * n ext2 block pointer, i.e. anything *except the superblock
 *
 */
void getlinsec_ext(char *buf, int sector, int sector_cnt)
{
        int ext_cnt = 0;
        
        if ( sector < SecPerClust ) {
                ext_cnt = SecPerClust - sector;
                memset(buf, 0, ext_cnt << SECTOR_SHIFT);
                buf += ext_cnt << SECTOR_SHIFT;
        }

        sector += ext_cnt;
        sector_cnt -= ext_cnt;
        getlinsec(buf, sector, sector_cnt);


}

void getonesec_ext(char *buf, int sector)
{
        getlinsec_ext(buf, sector, 1);
}




/**
 * get_group_desc:
 *
 * get the group's descriptor of group_num
 *
 * @param: group_num, the group number;
 * 
 * @return: the pointer of the group's descriptor
 *
 */ 
struct ext2_group_desc *get_group_desc(__u32 group_num)
{
        __u32 block_num;
        __u32 offset;
        struct ext2_group_desc *desc;
        struct cache_struct *cs;

        block_num = group_num / DescPerBlock;
        offset = group_num % DescPerBlock;

        block_num += sb.s_first_data_block + 1;
        cs = get_cache_block(block_num);

        desc = (struct ext2_group_desc *)cs->data + offset;

        return desc;
}


/**
 * read_inode:
 *
 * read the right inode structure to _dst_.
 *
 * @param: inode_offset, the inode offset within a group;
 * @prarm: dst, wher we will store the inode structure;
 * @param: desc, the pointer to the group's descriptor
 * @param: block, a pointer used for retruning the blk number for file structure
 * @param: offset, same as block
 *
 */
void read_inode(__u32 inode_offset, 
                struct ext2_inode *dst, struct ext2_group_desc *desc,
                __u32 *block, __u32 *offset)
{
        struct cache_struct *cs;
        struct ext2_inode *inode;
        
        *block  = inode_offset / InodePerBlock + desc->bg_inode_table;
        *offset = inode_offset % InodePerBlock;
        
        cs = get_cache_block(*block);

        /* well, in EXT4, the inode structure usually be 256 */
        inode = (struct ext2_inode *)(cs->data + (*offset * (sb.s_inode_size)));
        memcpy(dst, inode, EXT2_GOOD_OLD_INODE_SIZE);

        /* for file structure */
        *offset = (inode_offset * sb.s_inode_size) % ClustSize;
}






/**
 * open_inode:
 *
 * open a file indicated by an inode number in INR
 *
 * @param : inr, the inode number
 * @return: a open_file_t structure pointer
 *          file length in bytes
 *          the first 128 bytes of the inode
 *
 */
struct open_file_t * open_inode(unsigned int inr, __u32 *file_len)
{
        struct open_file_t *file;
        struct ext2_group_desc *desc;
        struct cache_struct *cs;

        __u32 inode_group, inode_offset;
        __u32 block_num, block_off;
                

        file = allocate_file();
        if ( !file )
                return NULL;

        file->file_sector = 0;
        
        inr --;
        inode_group  = inr / sb.s_inodes_per_group;
        
        /* get the group desc */
        desc = get_group_desc(inode_group);
        
        inode_offset = inr % sb.s_inodes_per_group;
        read_inode(inode_offset, &ThisInode, desc, &block_num, &block_off);
        
        /* Finally, we need to convet it to sector for now */
        file->file_in_sec = (block_num<<ClustShift) + (block_off>>SECTOR_SHIFT);
        file->file_in_off = block_off & (SECTOR_SIZE - 1);
        file->file_mode = ThisInode.i_mode;
        *file_len = file->file_bytesleft = ThisInode.i_size;
        
        if ( *file_len == 0 )
                return NULL;

        return file;
}


/**
 * close_file:
 *
 * Deallocates a file structure point by FILE
 *
 * @param: file, the file structure we want deallocate
 *
 */
void close_file(struct open_file_t *file)
{
        if ( file == NULL )
                return;

        file->file_bytesleft = 0;
        
}


struct ext4_extent_header * 
ext4_find_leaf (struct ext4_extent_header *eh, __u32 block)
{
        struct ext4_extent_idx *index;
        struct cache_struct *cs;
        __u64 blk;
        int i;
        char buf[ClustSize];

        while (1) {

                if (eh->eh_magic != EXT4_EXT_MAGIC)
                        return NULL;

                /* got it */
                if (eh->eh_depth == 0)
                        return eh;

                index = EXT4_FIRST_INDEX(eh);        


                for ( i = 0; i < eh->eh_entries; i++ ) {
                        if ( block < index[i].ei_block )
                                break;
                }

                if ( --i < 0 )
                        return NULL;

                blk = index[i].ei_leaf_hi;
                blk = (blk << 32) + index[i].ei_leaf_lo;
                
                /* read the blk to memeory */
                cs = get_cache_block(blk);
                
                eh = (struct ext4_extent_header *)(cs->data);
        }
}

/* handle the ext4 extents to get the phsical block number */
__u64 linsector_extent(__u32 block, struct ext2_inode *inode)
{
        struct ext4_extent_header *leaf;
        struct ext4_extent *ext;
        int i;
        __u64 start;

        leaf = ext4_find_leaf((struct ext4_extent_header*)inode->i_block,block);

        if (! leaf) {
                printf("ERROR, extent leaf not found\n");
                return 0;
        }


        ext = EXT4_FIRST_EXTENT(leaf);
        
        for ( i = 0; i < leaf->eh_entries; i++ ) {
                if ( block < ext[i].ee_block)
                        break;
        }


        if ( --i < 0 ) {
                printf("ERROR, not find the right block\n");
                return 0;
        }


        /* got it */
        block -= ext[i].ee_block;
        if ( block >= ext[i].ee_len)
                return 0;
        
        start = ext[i].ee_start_hi;
        start = (start << 32) + ext[i].ee_start_lo;
        
        return start + block;
}


/**
 * linsector_direct:
 * 
 * @param: block, the block index
 * @param: inode, the inode structure
 *
 * @return: the physic block number
 */
__u32 linsector_direct(__u32 block, struct ext2_inode *inode)
{
        struct cache_struct *cs;
        __u32 offset;

        
        /* direct blocks */
        if ( block < EXT2_NDIR_BLOCKS ) 
                return inode->i_block[block];


        /* indirect blocks */
        block -= EXT2_NDIR_BLOCKS;
        if ( block < PtrsPerBlock1 ) {
                __u32 ind_block = inode->i_block[EXT2_IND_BLOCK];


                cs = get_cache_block(ind_block);

                return ((__u32 *)cs->data)[block];
        }
        

        /* double indirect blocks */
        block -= PtrsPerBlock1;
        if ( block < PtrsPerBlock2 ) {
                __u32 dou_block = inode->i_block[EXT2_DIND_BLOCK];
                cs = get_cache_block(dou_block);
                
                dou_block = ( (__u32 *)cs->data )[block / PtrsPerBlock1];
                cs = get_cache_block(dou_block);

                return ( (__u32*)cs->data )[block % PtrsPerBlock1];
        }
        
        
        /* triple indirect block */
        block -= PtrsPerBlock2;
        if ( block < PtrsPerBlock3 ) {
                __u32 tri_block = inode->i_block[EXT2_TIND_BLOCK];
                cs = get_cache_block(tri_block);

                tri_block = ((__u32*)cs->data)[block / PtrsPerBlock2];
                cs = get_cache_block(tri_block);

                tri_block = ((__u32*)cs->data)[block % PtrsPerBlock2];
                cs = get_cache_block(tri_block);

                return ((__u32*)cs->data)[block % PtrsPerBlock1];
        }
        
        /* File too big, can not handle */
        printf("ERROR, file too big\n");
        return 0;
}
        
       
/**
 * linsector:
 *
 * Convert a linear sector index in a file to linear sector number
 *
 * well, alought this function converts a linear sector number to 
 * physic sector number, it uses block cache in the implemention.
 * 
 * @param: lin_sector, the lineral sector index
 * 
 * @return: physic sector number
 */
__u32 linsector(__u32 lin_sector)
{
        __u32 block = lin_sector >> ClustShift;
        struct ext2_inode *inode;

        /* well, this is what I think the variable ThisInode used for */
        inode = &ThisInode;

        if (inode->i_flags & EXT4_EXTENTS_FLAG)
                block = linsector_extent(block, inode);
        else
                block = (__u32)linsector_direct(block, inode);

        if ( !block ) {
                printf("WARNING: something error happend at linsector..\n");
                return 0;
        }

        /* finally convert it to sector */
        return ( (block << ClustShift) + (lin_sector & ClustMask) );
}


/**
 * getfssec:
 *
 * Get multiple sectors from a file 
 *
 * Alought we have made the buffer data based on block size, 
 * we use sector for implemention; because reading multiple 
 * sectors (then can be multiple blocks) is what the function 
 * do. So, let's be based on sectors.
 * 
 * same as above, execpt si is a pointer to a open_file_t
 *
 * @param: buf, the buffer to store data
 * @param: file, the pointer to open_file_t
 * @param: sectors, number of sectors to read
 * @param: have_more, used to indicate if there are more in the file
 *
 * @return: number of bytes read
 *
 */
int getfssec(char *buf, struct open_file_t *file, int sectors, int *have_more)
{
        int sector_left, next_sector, sector_idx;
        int frag_start, con_sec_cnt;
        int bytes_read = sectors << SECTOR_SHIFT;


        sector_left = (file->file_bytesleft + SECTOR_SIZE - 1) >> SECTOR_SHIFT;
        if ( sectors > sector_left )
                sectors = sector_left;
        
        do {
                /* get the frament */

                sector_idx  = file->file_sector;
                next_sector = frag_start = linsector(sector_idx);
                con_sec_cnt = 0;                
                
                do {
                        /* get the consective sectors count */
                        
                        con_sec_cnt ++;
                        sectors --;
                        if ( sectors <= 0 )
                                break;
                        
                        /***
                         * well, in Syslinux that means in real mode, there's a 
                         * 64k block limit, so we should need handle it here.
                         * 
                         * But it's a user program that test the driver, so we 
                         * don't need to do this here but should remember do it
                         * when we move into Sylinux.
                         */
                        sector_idx ++;
                        next_sector ++;
                }while( next_sector == linsector(sectors) );
                
                
                
#if 0           /* Debug message */
                printf("/**************************************************\n");
                printf("You are reading stores at sector --0x%x--0x%x\n", 
                       frag_start, frag_start + con_sec_cnt -1);
                printf("**************************************************/\n");
#endif
                
                getlinsec_ext(buf, frag_start, con_sec_cnt);
                buf += con_sec_cnt << 9;
                file->file_sector += con_sec_cnt;  /* next sector index */
        }while(sectors);
 

        if ( bytes_read >= file->file_bytesleft ) {
                bytes_read = file->file_bytesleft;
                close_file(file);
                *have_more = 0;
        } else {
                file->file_bytesleft -= bytes_read;
                *have_more = 1;
        }
        
        return bytes_read;        
}



/*
 * NOTE! unlike strncmp, ext2_match_entry returns 1 for success, 0 for failure.
 *
 * len <= EXT2_NAME_LEN and de != NULL are guaranteed by caller.
 */
static inline int ext2_match_entry (const char * const name,
					struct ext2_dir_entry * de)
{
	if (!de->d_inode)
		return 0;
	return !strncmp(name, de->d_name, de->d_name_len);
}


/*
 * p is at least 6 bytes before the end of page
 */
inline struct ext2_dir_entry *ext2_next_entry(struct ext2_dir_entry *p)
{
        return (struct ext2_dir_entry *)((char*)p + p->d_rec_len);
}



/**
 * find_dir_entry:
 *
 * find a dir entry, if find return it or return NULL
 *
 */
struct ext2_dir_entry* find_dir_entry(struct open_file_t *file, char *filename)
{
        int   have_more;
        struct ext2_dir_entry *de;

 
        EndBlock = (__u32 )trackbuf + (SecPerClust << SECTOR_SHIFT);
 
        /* read a clust at a time */
        getfssec(trackbuf, file, SecPerClust, &have_more);        
        de = (struct ext2_dir_entry *)trackbuf;        
        
        while ( 1 ) {
                if ( (char *)de >= (char *)EndBlock ) {
                        if (have_more) {
                                getfssec(trackbuf, file,SecPerClust,&have_more);
                                de = (struct ext2_dir_entry *)trackbuf;
                        } else
                                return NULL;
                }
                
                /* Zero inode == void entry */
                if ( de->d_inode == 0 ) {
                        de = ext2_next_entry(de);       
                        continue;
                }
                
                if ( ext2_match_entry (filename, de) ) {
                        filename += de->d_name_len;
                        if ( (*filename == 0) || (*filename == '/') )
                                return de;     /* got it */
                                                
                        /* not match, restore the filename then try next */
                        filename -= de->d_name_len;
                }
                                
                de = ext2_next_entry(de);
        } 
}


char* do_symlink(struct open_file_t *file, __u32 file_len, char *filename)
{
        int  flag, have_more;
   

        flag = ThisInode.i_file_acl ? SecPerClust : 0;
        
        if ( ThisInode.i_blocks == flag ) {
                /* fast symlink */
                close_file(file);          /* we've got all we need */
                memcpy(SymlinkTmpBuf, ThisInode.i_block, file_len);
                lnk_end = SymlinkTmpBuf + file_len;
                
        } else {                           
                /* slow symlink */
                getfssec(SymlinkTmpBuf,file,SYMLINK_SECTORS,&have_more);
                lnk_end = SymlinkTmpBuf + file_len;
        }
        
        /*
         * well, this happens like:
         * "/boot/xxx/y/z.abc" where xxx is a symlink to "/other/here"
         * so, we should get a new path name like:
         * "/other/here/y/z.abc"
         */
        if ( *filename != 0 )
                *lnk_end++ = '/';
        
        if ( strecpy(lnk_end, filename, SymlinkTmpBufEnd) ) 
                return NULL; /* buffer overflow */
                
        /*
         * now copy it to the "real" buffer; we need to have
         * two buffers so we avoid overwriting the tail on 
         * the next copy.
         */
        strcpy(SymlinkBuf, SymlinkTmpBuf);

        /* return the new path */
        return SymlinkBuf;
}




/**
 * searchdir:
 *
 * Search the root directory for a pre-mangle filename in FILENAME.
 *
 * @param: filename, the filename we want to search.
 *
 * @out  : a file pointer
 * @out  : file lenght in bytes
 *
 */
struct open_file_t* searchdir(char * filename, __u32 *file_len)
{
        struct open_file_t *file;
        struct ext2_dir_entry *de;
        __u8  file_mode;
        __u8  SymlinkCtr = MAX_SYMLINKS;        
        __u32 inr = CurrentDir;
        __u32 ThisDir;
        

 begin_path:
        while ( *filename == '/' ) { /* Absolute filename */
                inr = EXT2_ROOT_INO;
                filename ++;
        }
 open:
        if ( (file = open_inode(inr, file_len) ) == NULL )
                return NULL;
        
        file_mode = file->file_mode >> S_IFSHIFT;

        
        /* It's a file */
        if ( file_mode == T_IFREG ) {
                if ( *filename == '\0' )
                        goto done;
                else
                        goto err;
        } 
                
        
        /* It's a directory */
        if ( file_mode == T_IFDIR ) {                
                ThisDir = inr;
                
                if ( *filename == 0 )
                        goto err;
                while ( *filename == '/' )
                        filename ++;
        
                de = find_dir_entry(file, filename);
                if ( !de ) 
                        return NULL;

                inr = de->d_inode;
                filename += de->d_name_len;
                close(file);
                goto open;
        }


        
        /*
         * It's a symlink.  We have to determine if it's a fast symlink
         * (data stored in the inode) or not (data stored as a regular
         * file.)  Either which way, we start from the directory
         * which we just visited if relative, or from the root directory
         * if absolute, and append any remaining part of the path.
         */
        if ( file_mode == T_IFLNK ) {
                if ( --SymlinkCtr==0 || *file_len>=SYMLINK_SECTORS*SECTOR_SIZE)
                         goto err;    /* too many links or symlink too long */
                
                filename = do_symlink(file, *file_len, filename);
                if ( !filename )    
                        goto err_noclose;/* buffer overflow */
                                        
                inr = ThisDir;
                goto begin_path;     /* we got a new path, so search it again */
        }
        
        /* Otherwise, something bad ... */
 err:
        close_file(file);
 err_noclose:
        *file_len = 0;
        file = NULL;
 done:        
        return file;
}







/**
 * open:
 * 
 * open the file
 *
 * @param: filename
 *
 * @return: return 1 one successful, or 0
 *
 */
struct open_file_t* open_file(char *filename)
{
        struct open_file_t *file;
        struct getc_file *gc_file;
        int file_len;
        
        file = searchdir(filename, &file_len);
        if ( !file )
                return NULL;

        CurrentGetC -= getc_file_size;
        if ( (char *)CurrentGetC < GetCStack ) { /* Stack full */
                close_file(file);
                return NULL;
        }

        gc_file  = (struct getc_file *) CurrentGetC;
        gc_file->gc_file = file;
        gc_file->gc_bufbytes = 0;
        gc_file->gc_unget_cnt = 0;
                                               
        return file;
}


/**
 * read function:
 * return the bytes read
 */
int read_file(struct open_file_t *file, char *buf, int size, int *have_more)
{
        
        int sectors = (size + SECTOR_SIZE - 1) >> SECTOR_SHIFT;
        return getfssec(buf, file, sectors, have_more);
        
}

/**
 * init. the fs meta data, return the block size
 */
int init_fs()
{
        
        /* read the super block */
        getlinsec(&sb, 2, 2);

        ClustBytesShift = sb.s_log_block_size + 10;
        ClustSize = 1 << ClustBytesShift;
        ClustShift = ClustBytesShift - SECTOR_SHIFT;

        blk_size = ClustSize;
        DescPerBlock  = blk_size / ( 1 << ext2_group_desc_lg2size);
        InodePerBlock = blk_size / sb.s_inode_size;

        SecPerClust = ClustSize >> SECTOR_SHIFT;
        ClustMask = SecPerClust - 1;
        
        PtrsPerBlock1 = 1 << (ClustBytesShift - 2 );
        PtrsPerBlock2 = 1 << ( (ClustBytesShift - 2) * 2);
        PtrsPerBlock3 = 1 << ( (ClustBytesShift - 2) * 3);

        return blk_size;
}