minix/lib/libsffs/read.c

   1 /* This file contains file and directory reading file system call handlers.
   2  *
   3  * The entry points into this file are:
   4  *   do_read            perform the READ file system call
   5  *   do_getdents        perform the GETDENTS file system call
   6  *
   7  * Created:
   8  *   April 2009 (D.C. van Moolenbroek)
   9  */
  10
  11 #include "inc.h"
  12
  13 #include <dirent.h>
  14
  15 /*===========================================================================*
  16  *                              do_read                                      *
  17  *===========================================================================*/
  18 ssize_t do_read(ino_t ino_nr, struct fsdriver_data *data, size_t count,
  19         off_t pos, int call)
  20 {
  21 /* Read data from a file.
  22  */
  23   struct inode *ino;
  24   size_t size, off;
  25   char *ptr;
  26   int r, chunk;
  27
  28   if ((ino = find_inode(ino_nr)) == NULL)
  29         return EINVAL;
  30
  31   if (IS_DIR(ino)) return EISDIR;
  32
  33   if ((r = get_handle(ino)) != OK)
  34         return r;
  35
  36   assert(count > 0);
  37
  38   /* Use the buffer from below to eliminate extra copying. */
  39   size = sffs_table->t_readbuf(&ptr);
  40   off = 0;
  41
  42   while (count > 0) {
  43         chunk = MIN(count, size);
  44
  45         if ((r = sffs_table->t_read(ino->i_file, ptr, chunk, pos)) <= 0)
  46                 break;
  47
  48         chunk = r;
  49
  50         if ((r = fsdriver_copyout(data, off, ptr, chunk)) != OK)
  51                 break;
  52
  53         count -= chunk;
  54         off += chunk;
  55         pos += chunk;
  56   }
  57
  58   if (r < 0)
  59         return r;
  60
  61   return off;
  62 }
  63
  64 /*===========================================================================*
  65  *                              do_getdents                                  *
  66  *===========================================================================*/
  67 ssize_t do_getdents(ino_t ino_nr, struct fsdriver_data *data, size_t bytes,
  68         off_t *posp)
  69 {
  70 /* Retrieve directory entries.
  71  */
  72   struct fsdriver_dentry fsdentry;
  73   char name[NAME_MAX+1];
  74   struct inode *ino, *child;
  75   struct sffs_attr attr;
  76   off_t pos;
  77   int r;
  78   /* must be at least sizeof(struct dirent) + NAME_MAX */
  79   static char buf[BLOCK_SIZE];
  80
  81   if ((ino = find_inode(ino_nr)) == NULL)
  82         return EINVAL;
  83
  84   if (!IS_DIR(ino)) return ENOTDIR;
  85
  86   if (*posp < 0 || *posp >= ULONG_MAX) return EINVAL;
  87
  88   /* We are going to need at least one free inode to store children in. */
  89   if (!have_free_inode()) return ENFILE;
  90
  91   /* If we don't have a directory handle yet, get one now. */
  92   if ((r = get_handle(ino)) != OK)
  93         return r;
  94
  95   fsdriver_dentry_init(&fsdentry, data, bytes, buf, sizeof(buf));
  96
  97   /* We use the seek position as file index number. The first position is for
  98    * the "." entry, the second position is for the ".." entry, and the next
  99    * position numbers each represent a file in the directory.
 100    */
 101   for (;;) {
 102         /* Determine which inode and name to use for this entry.
 103          * We have no idea whether the host will give us "." and/or "..",
 104          * so generate our own and skip those from the host.
 105          */
 106         pos = (*posp)++;
 107
 108         if (pos == 0) {
 109                 /* Entry for ".". */
 110                 child = ino;
 111
 112                 strcpy(name, ".");
 113
 114                 get_inode(child);
 115         }
 116         else if (pos == 1) {
 117                 /* Entry for "..", but only when there is a parent. */
 118                 if (ino->i_parent == NULL)
 119                         continue;
 120
 121                 child = ino->i_parent;
 122
 123                 strcpy(name, "..");
 124
 125                 get_inode(child);
 126         }
 127         else {
 128                 /* Any other entry, not being "." or "..". */
 129                 attr.a_mask = SFFS_ATTR_MODE;
 130
 131                 r = sffs_table->t_readdir(ino->i_dir, pos - 2, name,
 132                         sizeof(name), &attr);
 133
 134                 if (r != OK) {
 135                         /* No more entries? Then close the handle and stop. */
 136                         if (r == ENOENT) {
 137                                 put_handle(ino);
 138
 139                                 break;
 140                         }
 141
 142                         /* FIXME: what if the error is ENAMETOOLONG? */
 143                         return r;
 144                 }
 145
 146                 if (!strcmp(name, ".") || !strcmp(name, ".."))
 147                         continue;
 148
 149                 if ((child = lookup_dentry(ino, name)) == NULL) {
 150                         child = get_free_inode();
 151
 152                         /* We were promised a free inode! */
 153                         assert(child != NULL);
 154
 155                         child->i_flags = MODE_TO_DIRFLAG(attr.a_mode);
 156
 157                         add_dentry(ino, name, child);
 158                 }
 159         }
 160
 161         r = fsdriver_dentry_add(&fsdentry, INODE_NR(child), name, strlen(name),
 162                 IS_DIR(child) ? DT_DIR : DT_REG);
 163
 164         put_inode(child);
 165
 166         if (r < 0)
 167                 return r;
 168         if (r == 0)
 169                 break;
 170   }
 171
 172   return fsdriver_dentry_finish(&fsdentry);
 173 }