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fsys_ext2fs.c

/*
 *  GRUB  --  GRand Unified Bootloader
 *  Copyright (C) 1999, 2001, 2003  Free Software Foundation, Inc.
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

#ifdef FSYS_EXT2FS

#include "shared.h"
#include "filesys.h"

static int mapblock1, mapblock2;

/* sizes are always in bytes, BLOCK values are always in DEV_BSIZE (sectors) */
#define DEV_BSIZE 512

/* include/linux/fs.h */
#define BLOCK_SIZE 1024       /* initial block size for superblock read */
/* made up, defaults to 1 but can be passed via mount_opts */
#define WHICH_SUPER 1
/* kind of from fs/ext2/super.c */
#define SBLOCK (WHICH_SUPER * BLOCK_SIZE / DEV_BSIZE) /* = 2 */

/* include/asm-i386/types.h */
typedef __signed__ char __s8;
typedef unsigned char __u8;
typedef __signed__ short __s16;
typedef unsigned short __u16;
typedef __signed__ int __s32;
typedef unsigned int __u32;

/*
 * Constants relative to the data blocks, from ext2_fs.h
 */
#define EXT2_NDIR_BLOCKS                12
#define EXT2_IND_BLOCK                  EXT2_NDIR_BLOCKS
#define EXT2_DIND_BLOCK                 (EXT2_IND_BLOCK + 1)
#define EXT2_TIND_BLOCK                 (EXT2_DIND_BLOCK + 1)
#define EXT2_N_BLOCKS                   (EXT2_TIND_BLOCK + 1)

/* include/linux/ext2_fs.h */
struct ext2_super_block
  {
    __u32 s_inodes_count;     /* Inodes count */
    __u32 s_blocks_count;     /* Blocks count */
    __u32 s_r_blocks_count;   /* Reserved blocks count */
    __u32 s_free_blocks_count;      /* Free blocks count */
    __u32 s_free_inodes_count;      /* Free inodes count */
    __u32 s_first_data_block; /* First Data Block */
    __u32 s_log_block_size;   /* Block size */
    __s32 s_log_frag_size;    /* Fragment size */
    __u32 s_blocks_per_group; /* # Blocks per group */
    __u32 s_frags_per_group;  /* # Fragments per group */
    __u32 s_inodes_per_group; /* # Inodes per group */
    __u32 s_mtime;            /* Mount time */
    __u32 s_wtime;            /* Write time */
    __u16 s_mnt_count;        /* Mount count */
    __s16 s_max_mnt_count;    /* Maximal mount count */
    __u16 s_magic;            /* Magic signature */
    __u16 s_state;            /* File system state */
    __u16 s_errors;           /* Behaviour when detecting errors */
    __u16 s_pad;
    __u32 s_lastcheck;        /* time of last check */
    __u32 s_checkinterval;    /* max. time between checks */
    __u32 s_creator_os;       /* OS */
    __u32 s_rev_level;        /* Revision level */
    __u16 s_def_resuid;       /* Default uid for reserved blocks */
    __u16 s_def_resgid;       /* Default gid for reserved blocks */
    __u32 s_reserved[235];    /* Padding to the end of the block */
  };

struct ext2_group_desc
  {
    __u32 bg_block_bitmap;    /* Blocks bitmap block */
    __u32 bg_inode_bitmap;    /* Inodes bitmap block */
    __u32 bg_inode_table;     /* Inodes table block */
    __u16 bg_free_blocks_count;     /* Free blocks count */
    __u16 bg_free_inodes_count;     /* Free inodes count */
    __u16 bg_used_dirs_count; /* Directories count */
    __u16 bg_pad;
    __u32 bg_reserved[3];
  };

struct ext2_inode
  {
    __u16 i_mode;       /* File mode */
    __u16 i_uid;        /* Owner Uid */
    __u32 i_size;       /* 4: Size in bytes */
    __u32 i_atime;            /* Access time */
    __u32 i_ctime;            /* 12: Creation time */
    __u32 i_mtime;            /* Modification time */
    __u32 i_dtime;            /* 20: Deletion Time */
    __u16 i_gid;        /* Group Id */
    __u16 i_links_count;      /* 24: Links count */
    __u32 i_blocks;           /* Blocks count */
    __u32 i_flags;            /* 32: File flags */
    union
      {
      struct
        {
          __u32 l_i_reserved1;
        }
      linux1;
      struct
        {
          __u32 h_i_translator;
        }
      hurd1;
      struct
        {
          __u32 m_i_reserved1;
        }
      masix1;
      }
    osd1;               /* OS dependent 1 */
    __u32 i_block[EXT2_N_BLOCKS];   /* 40: Pointers to blocks */
    __u32 i_version;          /* File version (for NFS) */
    __u32 i_file_acl;         /* File ACL */
    __u32 i_dir_acl;          /* Directory ACL */
    __u32 i_faddr;            /* Fragment address */
    union
      {
      struct
        {
          __u8 l_i_frag;      /* Fragment number */
          __u8 l_i_fsize;     /* Fragment size */
          __u16 i_pad1;
          __u32 l_i_reserved2[2];
        }
      linux2;
      struct
        {
          __u8 h_i_frag;      /* Fragment number */
          __u8 h_i_fsize;     /* Fragment size */
          __u16 h_i_mode_high;
          __u16 h_i_uid_high;
          __u16 h_i_gid_high;
          __u32 h_i_author;
        }
      hurd2;
      struct
        {
          __u8 m_i_frag;      /* Fragment number */
          __u8 m_i_fsize;     /* Fragment size */
          __u16 m_pad1;
          __u32 m_i_reserved2[2];
        }
      masix2;
      }
    osd2;               /* OS dependent 2 */
  };

/* linux/limits.h */
#define NAME_MAX         255  /* # chars in a file name */

/* linux/posix_type.h */
typedef long linux_off_t;

/* linux/ext2fs.h */
#define EXT2_NAME_LEN 255
struct ext2_dir_entry
  {
    __u32 inode;        /* Inode number */
    __u16 rec_len;            /* Directory entry length */
    __u8 name_len;            /* Name length */
    __u8 file_type;
    char name[EXT2_NAME_LEN]; /* File name */
  };

/* linux/ext2fs.h */
/*
 * EXT2_DIR_PAD defines the directory entries boundaries
 *
 * NOTE: It must be a multiple of 4
 */
#define EXT2_DIR_PAD                    4
#define EXT2_DIR_ROUND                  (EXT2_DIR_PAD - 1)
#define EXT2_DIR_REC_LEN(name_len)      (((name_len) + 8 + EXT2_DIR_ROUND) & \
                                         ~EXT2_DIR_ROUND)


/* ext2/super.c */
#define log2(n) ffz(~(n))

#define EXT2_SUPER_MAGIC      0xEF53      /* include/linux/ext2_fs.h */
#define EXT2_ROOT_INO              2      /* include/linux/ext2_fs.h */
#define PATH_MAX                1024      /* include/linux/limits.h */
#define MAX_LINK_COUNT             5      /* number of symbolic links to follow */

/* made up, these are pointers into FSYS_BUF */
/* read once, always stays there: */
#define SUPERBLOCK \
    ((struct ext2_super_block *)(FSYS_BUF))
#define GROUP_DESC \
    ((struct ext2_group_desc *) \
     ((int)SUPERBLOCK + sizeof(struct ext2_super_block)))
#define INODE \
    ((struct ext2_inode *)((int)GROUP_DESC + EXT2_BLOCK_SIZE(SUPERBLOCK)))
#define DATABLOCK1 \
    ((int)((int)INODE + sizeof(struct ext2_inode)))
#define DATABLOCK2 \
    ((int)((int)DATABLOCK1 + EXT2_BLOCK_SIZE(SUPERBLOCK)))

/* linux/ext2_fs.h */
#define EXT2_ADDR_PER_BLOCK(s)          (EXT2_BLOCK_SIZE(s) / sizeof (__u32))
#define EXT2_ADDR_PER_BLOCK_BITS(s)       (log2(EXT2_ADDR_PER_BLOCK(s)))

/* linux/ext2_fs.h */
#define EXT2_BLOCK_SIZE_BITS(s)        ((s)->s_log_block_size + 10)
/* kind of from ext2/super.c */
#define EXT2_BLOCK_SIZE(s)    (1 << EXT2_BLOCK_SIZE_BITS(s))
/* linux/ext2fs.h */
#define EXT2_DESC_PER_BLOCK(s) \
     (EXT2_BLOCK_SIZE(s) / sizeof (struct ext2_group_desc))
/* linux/stat.h */
#define S_IFMT  00170000
#define S_IFLNK  0120000
#define S_IFREG  0100000
#define S_IFDIR  0040000
#define S_ISLNK(m)      (((m) & S_IFMT) == S_IFLNK)
#define S_ISREG(m)      (((m) & S_IFMT) == S_IFREG)
#define S_ISDIR(m)      (((m) & S_IFMT) == S_IFDIR)

/* include/asm-i386/bitops.h */
/*
 * ffz = Find First Zero in word. Undefined if no zero exists,
 * so code should check against ~0UL first..
 */
static __inline__ unsigned long
ffz (unsigned long word)
{
  __asm__ ("bsfl %1,%0"
:        "=r" (word)
:        "r" (~word));
  return word;
}

/* check filesystem types and read superblock into memory buffer */
int
ext2fs_mount (void)
{
  int retval = 1;

  if ((((current_drive & 0x80) || (current_slice != 0))
       && (current_slice != PC_SLICE_TYPE_EXT2FS)
       && (current_slice != PC_SLICE_TYPE_LINUX_RAID)
       && (! IS_PC_SLICE_TYPE_BSD_WITH_FS (current_slice, FS_EXT2FS))
       && (! IS_PC_SLICE_TYPE_BSD_WITH_FS (current_slice, FS_OTHER)))
      || part_length < (SBLOCK + (sizeof (struct ext2_super_block) / DEV_BSIZE))
      || !devread (SBLOCK, 0, sizeof (struct ext2_super_block),
               (char *) SUPERBLOCK)
      || SUPERBLOCK->s_magic != EXT2_SUPER_MAGIC)
      retval = 0;

  return retval;
}

/* Takes a file system block number and reads it into BUFFER. */
static int
ext2_rdfsb (int fsblock, int buffer)
{
#ifdef E2DEBUG
  printf ("fsblock %d buffer %d\n", fsblock, buffer);
#endif /* E2DEBUG */
  return devread (fsblock * (EXT2_BLOCK_SIZE (SUPERBLOCK) / DEV_BSIZE), 0,
              EXT2_BLOCK_SIZE (SUPERBLOCK), (char *) buffer);
}

/* from
  ext2/inode.c:ext2_bmap()
*/
/* Maps LOGICAL_BLOCK (the file offset divided by the blocksize) into
   a physical block (the location in the file system) via an inode. */
static int
ext2fs_block_map (int logical_block)
{

#ifdef E2DEBUG
  unsigned char *i;
  for (i = (unsigned char *) INODE;
       i < ((unsigned char *) INODE + sizeof (struct ext2_inode));
       i++)
    {
      printf ("%c", "0123456789abcdef"[*i >> 4]);
      printf ("%c", "0123456789abcdef"[*i % 16]);
      if (!((i + 1 - (unsigned char *) INODE) % 16))
      {
        printf ("\n");
      }
      else
      {
        printf (" ");
      }
    }
  printf ("logical block %d\n", logical_block);
#endif /* E2DEBUG */

  /* if it is directly pointed to by the inode, return that physical addr */
  if (logical_block < EXT2_NDIR_BLOCKS)
    {
#ifdef E2DEBUG
      printf ("returning %d\n", (unsigned char *) (INODE->i_block[logical_block]));
      printf ("returning %d\n", INODE->i_block[logical_block]);
#endif /* E2DEBUG */
      return INODE->i_block[logical_block];
    }
  /* else */
  logical_block -= EXT2_NDIR_BLOCKS;
  /* try the indirect block */
  if (logical_block < EXT2_ADDR_PER_BLOCK (SUPERBLOCK))
    {
      if (mapblock1 != 1
        && !ext2_rdfsb (INODE->i_block[EXT2_IND_BLOCK], DATABLOCK1))
      {
        errnum = ERR_FSYS_CORRUPT;
        return -1;
      }
      mapblock1 = 1;
      return ((__u32 *) DATABLOCK1)[logical_block];
    }
  /* else */
  logical_block -= EXT2_ADDR_PER_BLOCK (SUPERBLOCK);
  /* now try the double indirect block */
  if (logical_block < (1 << (EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK) * 2)))
    {
      int bnum;
      if (mapblock1 != 2
        && !ext2_rdfsb (INODE->i_block[EXT2_DIND_BLOCK], DATABLOCK1))
      {
        errnum = ERR_FSYS_CORRUPT;
        return -1;
      }
      mapblock1 = 2;
      if ((bnum = (((__u32 *) DATABLOCK1)
               [logical_block >> EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK)]))
        != mapblock2
        && !ext2_rdfsb (bnum, DATABLOCK2))
      {
        errnum = ERR_FSYS_CORRUPT;
        return -1;
      }
      mapblock2 = bnum;
      return ((__u32 *) DATABLOCK2)
      [logical_block & (EXT2_ADDR_PER_BLOCK (SUPERBLOCK) - 1)];
    }
  /* else */
  mapblock2 = -1;
  logical_block -= (1 << (EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK) * 2));
  if (mapblock1 != 3
      && !ext2_rdfsb (INODE->i_block[EXT2_TIND_BLOCK], DATABLOCK1))
    {
      errnum = ERR_FSYS_CORRUPT;
      return -1;
    }
  mapblock1 = 3;
  if (!ext2_rdfsb (((__u32 *) DATABLOCK1)
               [logical_block >> (EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK)
                              * 2)],
               DATABLOCK2))
    {
      errnum = ERR_FSYS_CORRUPT;
      return -1;
    }
  if (!ext2_rdfsb (((__u32 *) DATABLOCK2)
               [(logical_block >> EXT2_ADDR_PER_BLOCK_BITS (SUPERBLOCK))
                & (EXT2_ADDR_PER_BLOCK (SUPERBLOCK) - 1)],
               DATABLOCK2))
    {
      errnum = ERR_FSYS_CORRUPT;
      return -1;
    }
  return ((__u32 *) DATABLOCK2)
    [logical_block & (EXT2_ADDR_PER_BLOCK (SUPERBLOCK) - 1)];
}

/* preconditions: all preconds of ext2fs_block_map */
int
ext2fs_read (char *buf, int len)
{
  int logical_block;
  int offset;
  int map;
  int ret = 0;
  int size = 0;

#ifdef E2DEBUG
  static char hexdigit[] = "0123456789abcdef";
  unsigned char *i;
  for (i = (unsigned char *) INODE;
       i < ((unsigned char *) INODE + sizeof (struct ext2_inode));
       i++)
    {
      printf ("%c", hexdigit[*i >> 4]);
      printf ("%c", hexdigit[*i % 16]);
      if (!((i + 1 - (unsigned char *) INODE) % 16))
      {
        printf ("\n");
      }
      else
      {
        printf (" ");
      }
    }
#endif /* E2DEBUG */
  while (len > 0)
    {
      /* find the (logical) block component of our location */
      logical_block = filepos >> EXT2_BLOCK_SIZE_BITS (SUPERBLOCK);
      offset = filepos & (EXT2_BLOCK_SIZE (SUPERBLOCK) - 1);
      map = ext2fs_block_map (logical_block);
#ifdef E2DEBUG
      printf ("map=%d\n", map);
#endif /* E2DEBUG */
      if (map < 0)
      break;

      size = EXT2_BLOCK_SIZE (SUPERBLOCK);
      size -= offset;
      if (size > len)
      size = len;

      disk_read_func = disk_read_hook;

      devread (map * (EXT2_BLOCK_SIZE (SUPERBLOCK) / DEV_BSIZE),
             offset, size, buf);

      disk_read_func = NULL;

      buf += size;
      len -= size;
      filepos += size;
      ret += size;
    }

  if (errnum)
    ret = 0;

  return ret;
}


/* Based on:
   def_blk_fops points to
   blkdev_open, which calls (I think):
   sys_open()
   do_open()
   open_namei()
   dir_namei() which accesses current->fs->root
     fs->root was set during original mount:
     (something)... which calls (I think):
     ext2_read_super()
     iget()
     __iget()
     read_inode()
     ext2_read_inode()
       uses desc_per_block_bits, which is set in ext2_read_super()
       also uses group descriptors loaded during ext2_read_super()
   lookup()
   ext2_lookup()
   ext2_find_entry()
   ext2_getblk()

*/

static inline
int ext2_is_fast_symlink (void)
{
  int ea_blocks;
  ea_blocks = INODE->i_file_acl ? EXT2_BLOCK_SIZE (SUPERBLOCK) / DEV_BSIZE : 0;
  return INODE->i_blocks == ea_blocks;
}

/* preconditions: ext2fs_mount already executed, therefore supblk in buffer
 *   known as SUPERBLOCK
 * returns: 0 if error, nonzero iff we were able to find the file successfully
 * postconditions: on a nonzero return, buffer known as INODE contains the
 *   inode of the file we were trying to look up
 * side effects: messes up GROUP_DESC buffer area
 */
int
ext2fs_dir (char *dirname)
{
  int current_ino = EXT2_ROOT_INO;  /* start at the root */
  int updir_ino = current_ino;      /* the parent of the current directory */
  int group_id;               /* which group the inode is in */
  int group_desc;       /* fs pointer to that group */
  int desc;             /* index within that group */
  int ino_blk;                /* fs pointer of the inode's information */
  int str_chk = 0;            /* used to hold the results of a string compare */
  struct ext2_group_desc *gdp;
  struct ext2_inode *raw_inode;     /* inode info corresponding to current_ino */

  char linkbuf[PATH_MAX];     /* buffer for following symbolic links */
  int link_count = 0;

  char *rest;
  char ch;              /* temp char holder */

  int off;              /* offset within block of directory entry (off mod blocksize) */
  int loc;              /* location within a directory */
  int blk;              /* which data blk within dir entry (off div blocksize) */
  long map;             /* fs pointer of a particular block from dir entry */
  struct ext2_dir_entry *dp;  /* pointer to directory entry */
#ifdef E2DEBUG
  unsigned char *i;
#endif      /* E2DEBUG */

  /* loop invariants:
     current_ino = inode to lookup
     dirname = pointer to filename component we are cur looking up within
     the directory known pointed to by current_ino (if any)
   */

  while (1)
    {
#ifdef E2DEBUG
      printf ("inode %d\n", current_ino);
      printf ("dirname=%s\n", dirname);
#endif /* E2DEBUG */

      /* look up an inode */
      group_id = (current_ino - 1) / (SUPERBLOCK->s_inodes_per_group);
      group_desc = group_id >> log2 (EXT2_DESC_PER_BLOCK (SUPERBLOCK));
      desc = group_id & (EXT2_DESC_PER_BLOCK (SUPERBLOCK) - 1);
#ifdef E2DEBUG
      printf ("ipg=%d, dpb=%d\n", SUPERBLOCK->s_inodes_per_group,
            EXT2_DESC_PER_BLOCK (SUPERBLOCK));
      printf ("group_id=%d group_desc=%d desc=%d\n", group_id, group_desc, desc);
#endif /* E2DEBUG */
      if (!ext2_rdfsb (
                  (WHICH_SUPER + group_desc + SUPERBLOCK->s_first_data_block),
                  (int) GROUP_DESC))
      {
        return 0;
      }
      gdp = GROUP_DESC;
      ino_blk = gdp[desc].bg_inode_table +
      (((current_ino - 1) % (SUPERBLOCK->s_inodes_per_group))
       >> log2 (EXT2_BLOCK_SIZE (SUPERBLOCK) / sizeof (struct ext2_inode)));
#ifdef E2DEBUG
      printf ("inode table fsblock=%d\n", ino_blk);
#endif /* E2DEBUG */
      if (!ext2_rdfsb (ino_blk, (int) INODE))
      {
        return 0;
      }

      /* reset indirect blocks! */
      mapblock2 = mapblock1 = -1;

      raw_inode = INODE +
      ((current_ino - 1)
       & (EXT2_BLOCK_SIZE (SUPERBLOCK) / sizeof (struct ext2_inode) - 1));
#ifdef E2DEBUG
      printf ("ipb=%d, sizeof(inode)=%d\n",
            (EXT2_BLOCK_SIZE (SUPERBLOCK) / sizeof (struct ext2_inode)),
            sizeof (struct ext2_inode));
      printf ("inode=%x, raw_inode=%x\n", INODE, raw_inode);
      printf ("offset into inode table block=%d\n", (int) raw_inode - (int) INODE);
      for (i = (unsigned char *) INODE; i <= (unsigned char *) raw_inode;
         i++)
      {
        printf ("%c", "0123456789abcdef"[*i >> 4]);
        printf ("%c", "0123456789abcdef"[*i % 16]);
        if (!((i + 1 - (unsigned char *) INODE) % 16))
          {
            printf ("\n");
          }
        else
          {
            printf (" ");
          }
      }
      printf ("first word=%x\n", *((int *) raw_inode));
#endif /* E2DEBUG */

      /* copy inode to fixed location */
      memcpy ((void *) INODE, (void *) raw_inode, sizeof (struct ext2_inode));

#ifdef E2DEBUG
      printf ("first word=%x\n", *((int *) INODE));
#endif /* E2DEBUG */

      /* If we've got a symbolic link, then chase it. */
      if (S_ISLNK (INODE->i_mode))
      {
        int len;
        if (++link_count > MAX_LINK_COUNT)
          {
            errnum = ERR_SYMLINK_LOOP;
            return 0;
          }

        /* Find out how long our remaining name is. */
        len = 0;
        while (dirname[len] && !isspace (dirname[len]))
          len++;

        /* Get the symlink size. */
        filemax = (INODE->i_size);
        if (filemax + len > sizeof (linkbuf) - 2)
          {
            errnum = ERR_FILELENGTH;
            return 0;
          }

        if (len)
          {
            /* Copy the remaining name to the end of the symlink data.
               Note that DIRNAME and LINKBUF may overlap! */
            memcpy (linkbuf + filemax, dirname, len);
          }
        linkbuf[filemax + len] = '\0';

        /* Read the symlink data. */
        if (! ext2_is_fast_symlink ())
          {
            /* Read the necessary blocks, and reset the file pointer. */
            len = grub_read (linkbuf, filemax);
            filepos = 0;
            if (!len)
            return 0;
          }
        else
          {
            /* Copy the data directly from the inode. */
            len = filemax;
            memcpy (linkbuf, (char *) INODE->i_block, len);
          }

#ifdef E2DEBUG
        printf ("symlink=%s\n", linkbuf);
#endif

        dirname = linkbuf;
        if (*dirname == '/')
          {
            /* It's an absolute link, so look it up in root. */
            current_ino = EXT2_ROOT_INO;
            updir_ino = current_ino;
          }
        else
          {
            /* Relative, so look it up in our parent directory. */
            current_ino = updir_ino;
          }

        /* Try again using the new name. */
        continue;
      }

      /* if end of filename, INODE points to the file's inode */
      if (!*dirname || isspace (*dirname))
      {
        if (!S_ISREG (INODE->i_mode))
          {
            errnum = ERR_BAD_FILETYPE;
            return 0;
          }

        filemax = (INODE->i_size);
        return 1;
      }

      /* else we have to traverse a directory */
      updir_ino = current_ino;

      /* skip over slashes */
      while (*dirname == '/')
      dirname++;

      /* if this isn't a directory of sufficient size to hold our file, abort */
      if (!(INODE->i_size) || !S_ISDIR (INODE->i_mode))
      {
        errnum = ERR_BAD_FILETYPE;
        return 0;
      }

      /* skip to next slash or end of filename (space) */
      for (rest = dirname; (ch = *rest) && !isspace (ch) && ch != '/';
         rest++);

      /* look through this directory and find the next filename component */
      /* invariant: rest points to slash after the next filename component */
      *rest = 0;
      loc = 0;

      do
      {

#ifdef E2DEBUG
        printf ("dirname=%s, rest=%s, loc=%d\n", dirname, rest, loc);
#endif /* E2DEBUG */

        /* if our location/byte offset into the directory exceeds the size,
           give up */
        if (loc >= INODE->i_size)
          {
            if (print_possibilities < 0)
            {
# if 0
              putchar ('\n');
# endif
            }
            else
            {
              errnum = ERR_FILE_NOT_FOUND;
              *rest = ch;
            }
            return (print_possibilities < 0);
          }

        /* else, find the (logical) block component of our location */
        blk = loc >> EXT2_BLOCK_SIZE_BITS (SUPERBLOCK);

        /* we know which logical block of the directory entry we are looking
           for, now we have to translate that to the physical (fs) block on
           the disk */
        map = ext2fs_block_map (blk);
#ifdef E2DEBUG
        printf ("fs block=%d\n", map);
#endif /* E2DEBUG */
        mapblock2 = -1;
        if ((map < 0) || !ext2_rdfsb (map, DATABLOCK2))
          {
            errnum = ERR_FSYS_CORRUPT;
            *rest = ch;
            return 0;
          }
        off = loc & (EXT2_BLOCK_SIZE (SUPERBLOCK) - 1);
        dp = (struct ext2_dir_entry *) (DATABLOCK2 + off);
        /* advance loc prematurely to next on-disk directory entry  */
        loc += dp->rec_len;

        /* NOTE: ext2fs filenames are NOT null-terminated */

#ifdef E2DEBUG
        printf ("directory entry ino=%d\n", dp->inode);
        if (dp->inode)
          printf ("entry=%s\n", dp->name);
#endif /* E2DEBUG */

        if (dp->inode)
          {
            int saved_c = dp->name[dp->name_len];

            dp->name[dp->name_len] = 0;
            str_chk = substring (dirname, dp->name);

# ifndef STAGE1_5
            if (print_possibilities && ch != '/'
              && (!*dirname || str_chk <= 0))
            {
              if (print_possibilities > 0)
                print_possibilities = -print_possibilities;
              print_a_completion (dp->name);
            }
# endif

            dp->name[dp->name_len] = saved_c;
          }

      }
      while (!dp->inode || (str_chk || (print_possibilities && ch != '/')));

      current_ino = dp->inode;
      *(dirname = rest) = ch;
    }
  /* never get here */
}

#endif /* FSYS_EXT2_FS */

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