servers/ext2/link.c

   1 /* Created (MFS based):
   2  *   February 2010 (Evgeniy Ivanov)
   3  */
   4
   5 #include "fs.h"
   6 #include <sys/stat.h>
   7 #include <string.h>
   8 #include <minix/com.h>
   9 #include "buf.h"
  10 #include "inode.h"
  11 #include "super.h"
  12 #include <minix/vfsif.h>
  13
  14 #define SAME 1000
  15
  16 static int freesp_inode(struct inode *rip, off_t st, off_t end);
  17 static int remove_dir(struct inode *rldirp, struct inode *rip, char
  18         dir_name[NAME_MAX + 1]);
  19 static int unlink_file(struct inode *dirp, struct inode *rip, char
  20         file_name[NAME_MAX + 1]);
  21 static off_t nextblock(off_t pos, int blocksize);
  22 static void zeroblock_half(struct inode *i, off_t p, int l);
  23 static void zeroblock_range(struct inode *i, off_t p, off_t h);
  24
  25 /* Args to zeroblock_half() */
  26 #define FIRST_HALF      0
  27 #define LAST_HALF       1
  28
  29
  30 /*===========================================================================*
  31  *                              fs_link                                      *
  32  *===========================================================================*/
  33 int fs_link()
  34 {
  35 /* Perform the link(name1, name2) system call. */
  36
  37   struct inode *ip, *rip;
  38   register int r;
  39   char string[NAME_MAX + 1];
  40   struct inode *new_ip;
  41   phys_bytes len;
  42
  43   /* Copy the link name's last component */
  44   len = fs_m_in.REQ_PATH_LEN; /* including trailing '\0' */
  45   if (len > NAME_MAX + 1 || len > EXT2_NAME_MAX + 1)
  46         return(ENAMETOOLONG);
  47
  48   r = sys_safecopyfrom(VFS_PROC_NR, (cp_grant_id_t) fs_m_in.REQ_GRANT, 0,
  49                        (vir_bytes) string, (size_t) len);
  50   if (r != OK) return r;
  51   NUL(string, len, sizeof(string));
  52
  53   /* Temporarily open the file. */
  54   if( (rip = get_inode(fs_dev, fs_m_in.REQ_INODE_NR)) == NULL)
  55           return(EINVAL);
  56
  57   /* Check to see if the file has maximum number of links already. */
  58   r = OK;
  59   if (rip->i_links_count >= USHRT_MAX)
  60           r = EMLINK;
  61   if(rip->i_links_count >= LINK_MAX)
  62           r = EMLINK;
  63
  64   /* Only super_user may link to directories. */
  65   if(r == OK)
  66           if( (rip->i_mode & I_TYPE) == I_DIRECTORY && caller_uid != SU_UID)
  67                   r = EPERM;
  68
  69   /* If error with 'name', return the inode. */
  70   if (r != OK) {
  71           put_inode(rip);
  72           return(r);
  73   }
  74
  75   /* Temporarily open the last dir */
  76   if( (ip = get_inode(fs_dev, fs_m_in.REQ_DIR_INO)) == NULL) {
  77         put_inode(rip);
  78         return(EINVAL);
  79   }
  80
  81   if (ip->i_links_count == NO_LINK) {   /* Dir does not actually exist */
  82         put_inode(rip);
  83         put_inode(ip);
  84         return(ENOENT);
  85   }
  86
  87   /* If 'name2' exists in full (even if no space) set 'r' to error. */
  88   if ((new_ip = advance(ip, string, IGN_PERM)) == NULL) {
  89         r = err_code;
  90         if(r == ENOENT)
  91                 r = OK;
  92   } else {
  93         put_inode(new_ip);
  94         r = EEXIST;
  95   }
  96
  97   /* Try to link. */
  98   if(r == OK)
  99           r = search_dir(ip, string, &rip->i_num, ENTER, IGN_PERM,
 100                          rip->i_mode & I_TYPE);
 101
 102   /* If success, register the linking. */
 103   if(r == OK) {
 104           rip->i_links_count++;
 105           rip->i_update |= CTIME;
 106           rip->i_dirt = IN_DIRTY;
 107   }
 108
 109   /* Done.  Release both inodes. */
 110   put_inode(rip);
 111   put_inode(ip);
 112   return(r);
 113 }
 114
 115
 116 /*===========================================================================*
 117  *                              fs_unlink                                    *
 118  *===========================================================================*/
 119 int fs_unlink()
 120 {
 121 /* Perform the unlink(name) or rmdir(name) system call. The code for these two
 122  * is almost the same.  They differ only in some condition testing.  Unlink()
 123  * may be used by the superuser to do dangerous things; rmdir() may not.
 124  */
 125   register struct inode *rip;
 126   struct inode *rldirp;
 127   int r;
 128   char string[NAME_MAX + 1];
 129   phys_bytes len;
 130
 131   /* Copy the last component */
 132   len = fs_m_in.REQ_PATH_LEN; /* including trailing '\0' */
 133   if (len > NAME_MAX + 1 || len > EXT2_NAME_MAX + 1)
 134         return(ENAMETOOLONG);
 135
 136   r = sys_safecopyfrom(VFS_PROC_NR, (cp_grant_id_t) fs_m_in.REQ_GRANT,
 137                        (vir_bytes) 0, (vir_bytes) string, (size_t) len);
 138   if (r != OK) return r;
 139   NUL(string, len, sizeof(string));
 140
 141   /* Temporarily open the dir. */
 142   if( (rldirp = get_inode(fs_dev, (ino_t) fs_m_in.REQ_INODE_NR)) == NULL)
 143           return(EINVAL);
 144
 145   /* The last directory exists.  Does the file also exist? */
 146   rip = advance(rldirp, string, IGN_PERM);
 147   r = err_code;
 148
 149   /* If error, return inode. */
 150   if(r != OK) {
 151         /* Mount point? */
 152         if (r == EENTERMOUNT || r == ELEAVEMOUNT) {
 153                 put_inode(rip);
 154                 r = EBUSY;
 155         }
 156         put_inode(rldirp);
 157         return(r);
 158   }
 159
 160   /* Now test if the call is allowed, separately for unlink() and rmdir(). */
 161   if(fs_m_in.m_type == REQ_UNLINK) {
 162           /* Only the su may unlink directories, but the su can unlink any
 163            * dir.*/
 164           if( (rip->i_mode & I_TYPE) == I_DIRECTORY) r = EPERM;
 165
 166           /* Actually try to unlink the file; fails if parent is mode 0 etc. */
 167           if (r == OK) r = unlink_file(rldirp, rip, string);
 168   } else {
 169           r = remove_dir(rldirp, rip, string); /* call is RMDIR */
 170   }
 171
 172   /* If unlink was possible, it has been done, otherwise it has not. */
 173   put_inode(rip);
 174   put_inode(rldirp);
 175   return(r);
 176 }
 177
 178
 179 /*===========================================================================*
 180  *                             fs_rdlink                                     *
 181  *===========================================================================*/
 182 int fs_rdlink()
 183 {
 184   block_t b;                   /* block containing link text */
 185   struct buf *bp = NULL;       /* buffer containing link text */
 186   char* link_text;             /* either bp->b_data or rip->i_block */
 187   register struct inode *rip;  /* target inode */
 188   register int r;              /* return value */
 189   size_t copylen;
 190
 191   copylen = min( (size_t) fs_m_in.REQ_MEM_SIZE, UMAX_FILE_POS);
 192
 193   /* Temporarily open the file. */
 194   if( (rip = get_inode(fs_dev, (ino_t) fs_m_in.REQ_INODE_NR)) == NULL)
 195           return(EINVAL);
 196
 197   if (rip->i_size >= MAX_FAST_SYMLINK_LENGTH) {
 198   /* normal symlink */
 199         if ((b = read_map(rip, (off_t) 0)) == NO_BLOCK) {
 200                 r = EIO;
 201         } else {
 202                 bp = get_block(rip->i_dev, b, NORMAL);
 203                 if (bp != NULL) {
 204                         link_text = b_data(bp);
 205                         r = OK;
 206                 } else {
 207                         r = EIO;
 208                 }
 209         }
 210   } else {
 211         /* fast symlink, stored in inode */
 212         link_text = (char*) rip->i_block;
 213         r = OK;
 214   }
 215   if (r == OK) {
 216   /* Passed all checks */
 217   /* We can safely cast to unsigned, because copylen is guaranteed to be
 218      below max file size */
 219         copylen = min( copylen, (unsigned) rip->i_size);
 220         r = sys_safecopyto(VFS_PROC_NR, (cp_grant_id_t) fs_m_in.REQ_GRANT,
 221                            (vir_bytes) 0, (vir_bytes) link_text,
 222                            (size_t) copylen);
 223         put_block(bp, DIRECTORY_BLOCK);
 224         if (r == OK)
 225                 fs_m_out.RES_NBYTES = copylen;
 226   }
 227
 228   put_inode(rip);
 229   return(r);
 230 }
 231
 232
 233 /*===========================================================================*
 234  *                              remove_dir                                   *
 235  *===========================================================================*/
 236 static int remove_dir(rldirp, rip, dir_name)
 237 struct inode *rldirp;                   /* parent directory */
 238 struct inode *rip;                      /* directory to be removed */
 239 char dir_name[NAME_MAX + 1];    /* name of directory to be removed */
 240 {
 241   /* A directory file has to be removed. Five conditions have to met:
 242    *    - The file must be a directory
 243    *    - The directory must be empty (except for . and ..)
 244    *    - The final component of the path must not be . or ..
 245    *    - The directory must not be the root of a mounted file system (VFS)
 246    *    - The directory must not be anybody's root/working directory (VFS)
 247    */
 248   int r;
 249
 250   /* search_dir checks that rip is a directory too. */
 251   if ((r = search_dir(rip, "", NULL, IS_EMPTY, IGN_PERM, 0)) != OK)
 252         return r;
 253
 254   if (strcmp(dir_name, ".") == 0 || strcmp(dir_name, "..") == 0)return(EINVAL);
 255   if (rip->i_num == ROOT_INODE) return(EBUSY); /* can't remove 'root' */
 256
 257   /* Actually try to unlink the file; fails if parent is mode 0 etc. */
 258   if ((r = unlink_file(rldirp, rip, dir_name)) != OK) return r;
 259
 260   /* Unlink . and .. from the dir. The super user can link and unlink any dir,
 261    * so don't make too many assumptions about them.
 262    */
 263   (void) unlink_file(rip, NULL, dot1);
 264   (void) unlink_file(rip, NULL, dot2);
 265   return(OK);
 266 }
 267
 268
 269 /*===========================================================================*
 270  *                              unlink_file                                  *
 271  *===========================================================================*/
 272 static int unlink_file(dirp, rip, file_name)
 273 struct inode *dirp;             /* parent directory of file */
 274 struct inode *rip;              /* inode of file, may be NULL too. */
 275 char file_name[NAME_MAX + 1]; /* name of file to be removed */
 276 {
 277 /* Unlink 'file_name'; rip must be the inode of 'file_name' or NULL. */
 278
 279   ino_t numb;                   /* inode number */
 280   int   r;
 281
 282   /* If rip is not NULL, it is used to get faster access to the inode. */
 283   if (rip == NULL) {
 284         /* Search for file in directory and try to get its inode. */
 285         err_code = search_dir(dirp, file_name, &numb, LOOK_UP, IGN_PERM, 0);
 286         if (err_code == OK) rip = get_inode(dirp->i_dev, (int) numb);
 287         if (err_code != OK || rip == NULL) return(err_code);
 288   } else {
 289         dup_inode(rip);         /* inode will be returned with put_inode */
 290   }
 291
 292   r = search_dir(dirp, file_name, NULL, DELETE, IGN_PERM, 0);
 293
 294   if (r == OK) {
 295         rip->i_links_count--;   /* entry deleted from parent's dir */
 296         rip->i_update |= CTIME;
 297         rip->i_dirt = IN_DIRTY;
 298   }
 299
 300   put_inode(rip);
 301   return(r);
 302 }
 303
 304
 305 /*===========================================================================*
 306  *                              fs_rename                                    *
 307  *===========================================================================*/
 308 int fs_rename()
 309 {
 310 /* Perform the rename(name1, name2) system call. */
 311   struct inode *old_dirp, *old_ip;      /* ptrs to old dir, file inodes */
 312   struct inode *new_dirp, *new_ip;      /* ptrs to new dir, file inodes */
 313   struct inode *new_superdirp, *next_new_superdirp;
 314   int r = OK;                           /* error flag; initially no error */
 315   int odir, ndir;                       /* TRUE iff {old|new} file is dir */
 316   int same_pdir;                        /* TRUE iff parent dirs are the same */
 317   char old_name[NAME_MAX + 1], new_name[NAME_MAX + 1];
 318   ino_t numb;
 319   phys_bytes len;
 320
 321   /* Copy the last component of the old name */
 322   len = fs_m_in.REQ_REN_LEN_OLD; /* including trailing '\0' */
 323   if (len > NAME_MAX + 1 || len > EXT2_NAME_MAX + 1)
 324         return(ENAMETOOLONG);
 325
 326   r = sys_safecopyfrom(VFS_PROC_NR, (cp_grant_id_t) fs_m_in.REQ_REN_GRANT_OLD,
 327                        (vir_bytes) 0, (vir_bytes) old_name, (size_t) len);
 328   if (r != OK) return r;
 329   NUL(old_name, len, sizeof(old_name));
 330
 331   /* Copy the last component of the new name */
 332   len = fs_m_in.REQ_REN_LEN_NEW; /* including trailing '\0' */
 333   if (len > NAME_MAX + 1 || len > EXT2_NAME_MAX + 1)
 334         return(ENAMETOOLONG);
 335
 336   r = sys_safecopyfrom(VFS_PROC_NR, (cp_grant_id_t) fs_m_in.REQ_REN_GRANT_NEW,
 337                        (vir_bytes) 0, (vir_bytes) new_name, (size_t) len);
 338   if (r != OK) return r;
 339   NUL(new_name, len, sizeof(new_name));
 340
 341   /* Get old dir inode */
 342   if( (old_dirp = get_inode(fs_dev, (ino_t) fs_m_in.REQ_REN_OLD_DIR)) == NULL)
 343         return(err_code);
 344
 345   old_ip = advance(old_dirp, old_name, IGN_PERM);
 346   r = err_code;
 347
 348   if (r == EENTERMOUNT || r == ELEAVEMOUNT) {
 349         put_inode(old_ip);
 350         old_ip = NULL;
 351         if (r == EENTERMOUNT) r = EXDEV;        /* should this fail at all? */
 352         else if (r == ELEAVEMOUNT) r = EINVAL;  /* rename on dot-dot */
 353   } else if (old_ip == NULL) {
 354         return(err_code);
 355   }
 356
 357   /* Get new dir inode */
 358   if( (new_dirp = get_inode(fs_dev, (ino_t) fs_m_in.REQ_REN_NEW_DIR)) == NULL) {
 359         put_inode(old_ip);
 360         put_inode(old_dirp);
 361         return(err_code);
 362   } else {
 363         if (new_dirp->i_links_count == NO_LINK) { /* Dir does not actually exist */
 364                 put_inode(old_ip);
 365                 put_inode(old_dirp);
 366                 put_inode(new_dirp);
 367                 return(ENOENT);
 368         }
 369   }
 370
 371   new_ip = advance(new_dirp, new_name, IGN_PERM); /* not required to exist */
 372
 373   /* However, if the check failed because the file does exist, don't continue.
 374    * Note that ELEAVEMOUNT is covered by the dot-dot check later. */
 375   if(err_code == EENTERMOUNT) {
 376         put_inode(new_ip);
 377         new_ip = NULL;
 378         r = EBUSY;
 379   }
 380
 381   if(old_ip != NULL)
 382           odir = ((old_ip->i_mode & I_TYPE) == I_DIRECTORY); /* TRUE iff dir */
 383   else
 384           odir = FALSE;
 385
 386   /* If it is ok, check for a variety of possible errors. */
 387   if(r == OK) {
 388         same_pdir = (old_dirp == new_dirp);
 389
 390         /* The old inode must not be a superdirectory of the new last dir. */
 391         if (odir && !same_pdir) {
 392                 dup_inode(new_superdirp = new_dirp);
 393                 while (TRUE) {  /* may hang in a file system loop */
 394                         if (new_superdirp == old_ip) {
 395                                 put_inode(new_superdirp);
 396                                 r = EINVAL;
 397                                 break;
 398                         }
 399                         next_new_superdirp = advance(new_superdirp, dot2,
 400                                                      IGN_PERM);
 401
 402                         put_inode(new_superdirp);
 403                         if(next_new_superdirp == new_superdirp) {
 404                                 put_inode(new_superdirp);
 405                                 break;
 406                         }
 407                         if(err_code == ELEAVEMOUNT) {
 408                                 /* imitate that we are back at the root,
 409                                  * cross device checked already on VFS */
 410                                 put_inode(next_new_superdirp);
 411                                 err_code = OK;
 412                                 break;
 413                         }
 414                         new_superdirp = next_new_superdirp;
 415                         if(new_superdirp == NULL) {
 416                                 /* Missing ".." entry.  Assume the worst. */
 417                                 r = EINVAL;
 418                                 break;
 419                         }
 420                 }
 421         }
 422
 423         /* The old or new name must not be . or .. */
 424         if(strcmp(old_name, ".") == 0 || strcmp(old_name, "..") == 0 ||
 425            strcmp(new_name, ".") == 0 || strcmp(new_name, "..") == 0) {
 426                 r = EINVAL;
 427         }
 428         /* Both parent directories must be on the same device.
 429         if(old_dirp->i_dev != new_dirp->i_dev) r = EXDEV; */
 430
 431         /* Some tests apply only if the new path exists. */
 432         if(new_ip == NULL) {
 433                 /* don't rename a file with a file system mounted on it.
 434                 if (old_ip->i_dev != old_dirp->i_dev) r = EXDEV;*/
 435                 if(odir && (new_dirp->i_links_count >= SHRT_MAX ||
 436                             new_dirp->i_links_count >= LINK_MAX) &&
 437                    !same_pdir && r == OK) {
 438                         r = EMLINK;
 439                 }
 440         } else {
 441                 if(old_ip == new_ip) r = SAME; /* old=new */
 442
 443                 ndir = ((new_ip->i_mode & I_TYPE) == I_DIRECTORY);/* dir ? */
 444                 if(odir == TRUE && ndir == FALSE) r = ENOTDIR;
 445                 if(odir == FALSE && ndir == TRUE) r = EISDIR;
 446         }
 447   }
 448
 449   /* If a process has another root directory than the system root, we might
 450    * "accidently" be moving it's working directory to a place where it's
 451    * root directory isn't a super directory of it anymore. This can make
 452    * the function chroot useless. If chroot will be used often we should
 453    * probably check for it here. */
 454
 455   /* The rename will probably work. Only two things can go wrong now:
 456    * 1. being unable to remove the new file. (when new file already exists)
 457    * 2. being unable to make the new directory entry. (new file doesn't exists)
 458    *     [directory has to grow by one block and cannot because the disk
 459    *      is completely full].
 460    */
 461   if(r == OK) {
 462         if(new_ip != NULL) {
 463                 /* There is already an entry for 'new'. Try to remove it. */
 464                 if(odir)
 465                         r = remove_dir(new_dirp, new_ip, new_name);
 466                 else
 467                         r = unlink_file(new_dirp, new_ip, new_name);
 468         }
 469         /* if r is OK, the rename will succeed, while there is now an
 470          * unused entry in the new parent directory. */
 471   }
 472
 473   if(r == OK) {
 474           /* If the new name will be in the same parent directory as the old
 475            * one, first remove the old name to free an entry for the new name,
 476            * otherwise first try to create the new name entry to make sure
 477            * the rename will succeed.
 478            */
 479         numb = old_ip->i_num;           /* inode number of old file */
 480
 481         if(same_pdir) {
 482                 r = search_dir(old_dirp,old_name, NULL, DELETE,IGN_PERM, 0);
 483                                                 /* shouldn't go wrong. */
 484                 if(r == OK)
 485                         (void) search_dir(old_dirp, new_name, &numb, ENTER, IGN_PERM,
 486                                           old_ip->i_mode & I_TYPE);
 487         } else {
 488                 r = search_dir(new_dirp, new_name, &numb, ENTER, IGN_PERM,
 489                                         old_ip->i_mode & I_TYPE);
 490                 if(r == OK)
 491                         (void) search_dir(old_dirp, old_name, (ino_t *) 0, DELETE,
 492                                           IGN_PERM, 0);
 493         }
 494   }
 495   /* If r is OK, the ctime and mtime of old_dirp and new_dirp have been marked
 496    * for update in search_dir. */
 497
 498   if(r == OK && odir && !same_pdir) {
 499         /* Update the .. entry in the directory (still points to old_dirp).*/
 500         numb = new_dirp->i_num;
 501         (void) unlink_file(old_ip, NULL, dot2);
 502         if(search_dir(old_ip, dot2, &numb, ENTER, IGN_PERM, I_DIRECTORY) == OK) {
 503                 /* New link created. */
 504                 new_dirp->i_links_count++;
 505                 new_dirp->i_dirt = IN_DIRTY;
 506         }
 507   }
 508
 509   /* Release the inodes. */
 510   put_inode(old_dirp);
 511   put_inode(old_ip);
 512   put_inode(new_dirp);
 513   put_inode(new_ip);
 514   return(r == SAME ? OK : r);
 515 }
 516
 517
 518 /*===========================================================================*
 519  *                              fs_ftrunc                                    *
 520  *===========================================================================*/
 521 int fs_ftrunc(void)
 522 {
 523   struct inode *rip;
 524   off_t start, end;
 525   int r;
 526
 527   if( (rip = find_inode(fs_dev, (ino_t) fs_m_in.REQ_INODE_NR)) == NULL)
 528           return(EINVAL);
 529
 530   start = fs_m_in.REQ_TRC_START_LO;
 531   end = fs_m_in.REQ_TRC_END_LO;
 532
 533   if (end == 0)
 534           r = truncate_inode(rip, start);
 535   else
 536           r = freesp_inode(rip, start, end);
 537
 538   return(r);
 539 }
 540
 541
 542 /*===========================================================================*
 543  *                              truncate_inode                               *
 544  *===========================================================================*/
 545 int truncate_inode(rip, newsize)
 546 register struct inode *rip;     /* pointer to inode to be truncated */
 547 off_t newsize;                  /* inode must become this size */
 548 {
 549 /* Set inode to a certain size, freeing any blocks no longer referenced
 550  * and updating the size in the inode. If the inode is extended, the
 551  * extra space is a hole that reads as zeroes.
 552  *
 553  * Nothing special has to happen to file pointers if inode is opened in
 554  * O_APPEND mode, as this is different per fd and is checked when
 555  * writing is done.
 556  */
 557   int r;
 558   mode_t file_type;
 559
 560   discard_preallocated_blocks(rip);
 561
 562   file_type = rip->i_mode & I_TYPE;     /* check to see if file is special */
 563   if (file_type == I_CHAR_SPECIAL || file_type == I_BLOCK_SPECIAL)
 564         return(EINVAL);
 565   if (newsize > rip->i_sp->s_max_size)  /* don't let inode grow too big */
 566         return(EFBIG);
 567
 568   /* Free the actual space if truncating. */
 569   if (newsize < rip->i_size) {
 570         if ((r = freesp_inode(rip, newsize, rip->i_size)) != OK)
 571                 return(r);
 572   }
 573
 574   /* Clear the rest of the last block if expanding. */
 575   if (newsize > rip->i_size) zeroblock_half(rip, rip->i_size, LAST_HALF);
 576
 577   /* Next correct the inode size. */
 578   rip->i_size = newsize;
 579   rip->i_update |= CTIME | MTIME;
 580   rip->i_dirt = IN_DIRTY;
 581
 582   return(OK);
 583 }
 584
 585
 586 /*===========================================================================*
 587  *                              freesp_inode                                 *
 588  *===========================================================================*/
 589 static int freesp_inode(rip, start, end)
 590 register struct inode *rip;     /* pointer to inode to be partly freed */
 591 off_t start, end;               /* range of bytes to free (end uninclusive) */
 592 {
 593 /* Cut an arbitrary hole in an inode. The caller is responsible for checking
 594  * the reasonableness of the inode type of rip. The reason is this is that
 595  * this function can be called for different reasons, for which different
 596  * sets of inode types are reasonable. Adjusting the final size of the inode
 597  * is to be done by the caller too, if wished.
 598  *
 599  * Consumers of this function currently are truncate_inode() (used to
 600  * free indirect and data blocks for any type of inode, but also to
 601  * implement the ftruncate() and truncate() system calls) and the F_FREESP
 602  * fcntl().
 603  */
 604   off_t p, e;
 605   int r;
 606   unsigned short block_size = rip->i_sp->s_block_size;
 607   int zero_last, zero_first;
 608
 609   discard_preallocated_blocks(rip);
 610
 611   if (rip->i_blocks == 0) {
 612   /* Either hole or symlink. Freeing fast symlink using
 613    * write_map() causes segfaults since it doesn't use any
 614    * blocks, but uses i_block[] to store target.
 615    */
 616         return(OK);
 617   }
 618
 619   if(end > rip->i_size)         /* freeing beyond end makes no sense */
 620         end = rip->i_size;
 621   if(end <= start)              /* end is uninclusive, so start<end */
 622         return(EINVAL);
 623
 624   /* If freeing doesn't cross a block boundary, then we may only zero
 625    * a range of the block.
 626    */
 627   zero_last = start % block_size;
 628   zero_first = end % block_size && end < rip->i_size;
 629   if (start/block_size == (end-1)/block_size && (zero_last || zero_first)) {
 630         zeroblock_range(rip, start, end-start);
 631   } else {
 632         /* First zero unused part of partly used blocks. */
 633         if (zero_last)
 634                 zeroblock_half(rip, start, LAST_HALF);
 635         if (zero_first)
 636                 zeroblock_half(rip, end, FIRST_HALF);
 637
 638         /* Now completely free the completely unused blocks.
 639          * write_map() will free unused indirect
 640          * blocks too. Converting the range to block numbers avoids
 641          * overflow on p when doing e.g. 'p += block_size'.
 642          */
 643         e = end / block_size;
 644         if (end == rip->i_size && (end % block_size))
 645                 e++;
 646         for (p = nextblock(start, block_size)/block_size; p < e; p++) {
 647                 if ((r = write_map(rip, p*block_size, NO_BLOCK, WMAP_FREE)) != OK)
 648                         return(r);
 649         }
 650   }
 651
 652   rip->i_update |= CTIME | MTIME;
 653   rip->i_dirt = IN_DIRTY;
 654
 655   return(OK);
 656 }
 657
 658
 659 /*===========================================================================*
 660  *                              nextblock                                    *
 661  *===========================================================================*/
 662 static off_t nextblock(pos, block_size)
 663 off_t pos;
 664 unsigned short block_size;
 665 {
 666 /* Return the first position in the next block after position 'pos'
 667  * (unless this is the first position in the current block).
 668  * This can be done in one expression, but that can overflow pos.
 669  */
 670   off_t p;
 671   p = (pos / block_size) * block_size;
 672   if (pos % block_size) p += block_size;        /* Round up. */
 673   return(p);
 674 }
 675
 676
 677 /*===========================================================================*
 678  *                              zeroblock_half                               *
 679  *===========================================================================*/
 680 static void zeroblock_half(rip, pos, half)
 681 struct inode *rip;
 682 off_t pos;
 683 int half;
 684 {
 685 /* Zero the upper or lower 'half' of a block that holds position 'pos'.
 686  * half can be FIRST_HALF or LAST_HALF.
 687  *
 688  * FIRST_HALF: 0..pos-1 will be zeroed
 689  * LAST_HALF:  pos..blocksize-1 will be zeroed
 690  */
 691   off_t offset, len;
 692
 693   /* Offset of zeroing boundary. */
 694   offset = pos % rip->i_sp->s_block_size;
 695
 696   if(half == LAST_HALF)  {
 697         len = rip->i_sp->s_block_size - offset;
 698   } else {
 699         len = offset;
 700         pos -= offset;
 701   }
 702
 703   zeroblock_range(rip, pos, len);
 704 }
 705
 706
 707 /*===========================================================================*
 708  *                              zeroblock_range                              *
 709  *===========================================================================*/
 710 static void zeroblock_range(rip, pos, len)
 711 struct inode *rip;
 712 off_t pos;
 713 off_t len;
 714 {
 715 /* Zero a range in a block.
 716  * This function is used to zero a segment of a block.
 717  */
 718   block_t b;
 719   struct buf *bp;
 720   off_t offset;
 721
 722   if (!len) return; /* no zeroing to be done. */
 723   if ( (b = read_map(rip, pos)) == NO_BLOCK) return;
 724   if ( (bp = get_block(rip->i_dev, b, NORMAL)) == NULL)
 725         panic("zeroblock_range: no block");
 726   offset = pos % rip->i_sp->s_block_size;
 727   if (offset + len > rip->i_sp->s_block_size)
 728         panic("zeroblock_range: len too long", len);
 729   memset(b_data(bp) + offset, 0, len);
 730   lmfs_markdirty(bp);
 731   put_block(bp, FULL_DATA_BLOCK);
 732 }