From c6e3baa565bc3b5828cf0d67ca6429dbe5f8687c Mon Sep 17 00:00:00 2001 From: Rob Clark Date: Sat, 9 Sep 2017 13:15:53 -0400 Subject: fs/fat: introduce new director iterators MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Untangle directory traversal into a simple iterator, to replace the existing multi-purpose do_fat_read_at() + get_dentfromdir(). Signed-off-by: Rob Clark Reviewed-by: Łukasz Majewski --- fs/fat/fat.c | 356 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 353 insertions(+), 3 deletions(-) (limited to 'fs/fat') diff --git a/fs/fat/fat.c b/fs/fat/fat.c index e1c0a15dc7..ee2bbe38f1 100644 --- a/fs/fat/fat.c +++ b/fs/fat/fat.c @@ -812,7 +812,6 @@ static int get_fs_info(fsdata *mydata) { boot_sector bs; volume_info volinfo; - __u32 root_cluster = 0; int ret; ret = read_bootsectandvi(&bs, &volinfo, &mydata->fatsize); @@ -822,7 +821,6 @@ static int get_fs_info(fsdata *mydata) } if (mydata->fatsize == 32) { - root_cluster = bs.root_cluster; mydata->fatlength = bs.fat32_length; } else { mydata->fatlength = bs.fat_length; @@ -843,6 +841,7 @@ static int get_fs_info(fsdata *mydata) if (mydata->fatsize == 32) { mydata->data_begin = mydata->rootdir_sect - (mydata->clust_size * 2); + mydata->root_cluster = bs.root_cluster; } else { mydata->rootdir_size = ((bs.dir_entries[1] * (int)256 + bs.dir_entries[0]) * @@ -851,6 +850,9 @@ static int get_fs_info(fsdata *mydata) mydata->data_begin = mydata->rootdir_sect + mydata->rootdir_size - (mydata->clust_size * 2); + mydata->root_cluster = (mydata->rootdir_sect - + mydata->data_begin) / + mydata->clust_size; } mydata->fatbufnum = -1; @@ -868,7 +870,7 @@ static int get_fs_info(fsdata *mydata) mydata->fatsize, mydata->fat_sect, mydata->fatlength); debug("Rootdir begins at cluster: %d, sector: %d, offset: %x\n" "Data begins at: %d\n", - root_cluster, + mydata->root_cluster, mydata->rootdir_sect, mydata->rootdir_sect * mydata->sect_size, mydata->data_begin); debug("Sector size: %d, cluster size: %d\n", mydata->sect_size, @@ -1245,6 +1247,354 @@ exit: return ret; } + +/* + * Directory iterator, to simplify filesystem traversal + * + * Implements an iterator pattern to traverse directory tables, + * transparently handling directory tables split across multiple + * clusters, and the difference between FAT12/FAT16 root directory + * (contiguous) and subdirectories + FAT32 root (chained). + * + * Rough usage: + * + * for (fat_itr_root(&itr, fsdata); fat_itr_next(&itr); ) { + * // to traverse down to a subdirectory pointed to by + * // current iterator position: + * fat_itr_child(&itr, &itr); + * } + * + * For more complete example, see fat_itr_resolve() + */ + +typedef struct { + fsdata *fsdata; /* filesystem parameters */ + unsigned clust; /* current cluster */ + int last_cluster; /* set once we've read last cluster */ + int is_root; /* is iterator at root directory */ + int remaining; /* remaining dent's in current cluster */ + + /* current iterator position values: */ + dir_entry *dent; /* current directory entry */ + char l_name[VFAT_MAXLEN_BYTES]; /* long (vfat) name */ + char s_name[14]; /* short 8.3 name */ + char *name; /* l_name if there is one, else s_name */ + + /* storage for current cluster in memory: */ + u8 block[MAX_CLUSTSIZE] __aligned(ARCH_DMA_MINALIGN); +} fat_itr; + +static int fat_itr_isdir(fat_itr *itr); + +/** + * fat_itr_root() - initialize an iterator to start at the root + * directory + * + * @itr: iterator to initialize + * @fsdata: filesystem data for the partition + * @return 0 on success, else -errno + */ +static int fat_itr_root(fat_itr *itr, fsdata *fsdata) +{ + if (get_fs_info(fsdata)) + return -ENXIO; + + itr->fsdata = fsdata; + itr->clust = fsdata->root_cluster; + itr->dent = NULL; + itr->remaining = 0; + itr->last_cluster = 0; + itr->is_root = 1; + + return 0; +} + +/** + * fat_itr_child() - initialize an iterator to descend into a sub- + * directory + * + * Initializes 'itr' to iterate the contents of the directory at + * the current cursor position of 'parent'. It is an error to + * call this if the current cursor of 'parent' is pointing at a + * regular file. + * + * Note that 'itr' and 'parent' can be the same pointer if you do + * not need to preserve 'parent' after this call, which is useful + * for traversing directory structure to resolve a file/directory. + * + * @itr: iterator to initialize + * @parent: the iterator pointing at a directory entry in the + * parent directory of the directory to iterate + */ +static void fat_itr_child(fat_itr *itr, fat_itr *parent) +{ + fsdata *mydata = parent->fsdata; /* for silly macros */ + unsigned clustnum = START(parent->dent); + + assert(fat_itr_isdir(parent)); + + itr->fsdata = parent->fsdata; + if (clustnum > 0) { + itr->clust = clustnum; + } else { + itr->clust = parent->fsdata->root_cluster; + } + itr->dent = NULL; + itr->remaining = 0; + itr->last_cluster = 0; + itr->is_root = 0; +} + +static void *next_cluster(fat_itr *itr) +{ + fsdata *mydata = itr->fsdata; /* for silly macros */ + int ret; + u32 sect; + + /* have we reached the end? */ + if (itr->last_cluster) + return NULL; + + sect = clust_to_sect(itr->fsdata, itr->clust); + + debug("FAT read(sect=%d), clust_size=%d, DIRENTSPERBLOCK=%zd\n", + sect, itr->fsdata->clust_size, DIRENTSPERBLOCK); + + /* + * NOTE: do_fat_read_at() had complicated logic to deal w/ + * vfat names that span multiple clusters in the fat16 case, + * which get_dentfromdir() probably also needed (and was + * missing). And not entirely sure what fat32 didn't have + * the same issue.. We solve that by only caring about one + * dent at a time and iteratively constructing the vfat long + * name. + */ + ret = disk_read(sect, itr->fsdata->clust_size, + itr->block); + if (ret < 0) { + debug("Error: reading block\n"); + return NULL; + } + + if (itr->is_root && itr->fsdata->fatsize != 32) { + itr->clust++; + sect = clust_to_sect(itr->fsdata, itr->clust); + if (sect - itr->fsdata->rootdir_sect >= + itr->fsdata->rootdir_size) { + debug("cursect: 0x%x\n", itr->clust); + itr->last_cluster = 1; + } + } else { + itr->clust = get_fatent(itr->fsdata, itr->clust); + if (CHECK_CLUST(itr->clust, itr->fsdata->fatsize)) { + debug("cursect: 0x%x\n", itr->clust); + itr->last_cluster = 1; + } + } + + return itr->block; +} + +static dir_entry *next_dent(fat_itr *itr) +{ + if (itr->remaining == 0) { + struct dir_entry *dent = next_cluster(itr); + unsigned nbytes = itr->fsdata->sect_size * + itr->fsdata->clust_size; + + /* have we reached the last cluster? */ + if (!dent) + return NULL; + + itr->remaining = nbytes / sizeof(dir_entry) - 1; + itr->dent = dent; + } else { + itr->remaining--; + itr->dent++; + } + + /* have we reached the last valid entry? */ + if (itr->dent->name[0] == 0) + return NULL; + + return itr->dent; +} + +static dir_entry *extract_vfat_name(fat_itr *itr) +{ + struct dir_entry *dent = itr->dent; + int seqn = itr->dent->name[0] & ~LAST_LONG_ENTRY_MASK; + u8 chksum, alias_checksum = ((dir_slot *)dent)->alias_checksum; + int n = 0; + + while (seqn--) { + char buf[13]; + int idx = 0; + + slot2str((dir_slot *)dent, buf, &idx); + + /* shift accumulated long-name up and copy new part in: */ + memmove(itr->l_name + idx, itr->l_name, n); + memcpy(itr->l_name, buf, idx); + n += idx; + + dent = next_dent(itr); + if (!dent) + return NULL; + } + + itr->l_name[n] = '\0'; + + chksum = mkcksum(dent->name, dent->ext); + + /* checksum mismatch could mean deleted file, etc.. skip it: */ + if (chksum != alias_checksum) { + debug("** chksum=%x, alias_checksum=%x, l_name=%s, s_name=%8s.%3s\n", + chksum, alias_checksum, itr->l_name, dent->name, dent->ext); + return NULL; + } + + return dent; +} + +/** + * fat_itr_next() - step to the next entry in a directory + * + * Must be called once on a new iterator before the cursor is valid. + * + * @itr: the iterator to iterate + * @return boolean, 1 if success or 0 if no more entries in the + * current directory + */ +static int fat_itr_next(fat_itr *itr) +{ + dir_entry *dent; + + itr->name = NULL; + + while (1) { + dent = next_dent(itr); + if (!dent) + return 0; + + if (dent->name[0] == DELETED_FLAG || + dent->name[0] == aRING) + continue; + + if (dent->attr & ATTR_VOLUME) { + if (vfat_enabled && + (dent->attr & ATTR_VFAT) == ATTR_VFAT && + (dent->name[0] & LAST_LONG_ENTRY_MASK)) { + dent = extract_vfat_name(itr); + if (!dent) + continue; + itr->name = itr->l_name; + break; + } else { + /* Volume label or VFAT entry, skip */ + continue; + } + } + + break; + } + + get_name(dent, itr->s_name); + if (!itr->name) + itr->name = itr->s_name; + + return 1; +} + +/** + * fat_itr_isdir() - is current cursor position pointing to a directory + * + * @itr: the iterator + * @return true if cursor is at a directory + */ +static int fat_itr_isdir(fat_itr *itr) +{ + return !!(itr->dent->attr & ATTR_DIR); +} + +/* + * Helpers: + */ + +#define TYPE_FILE 0x1 +#define TYPE_DIR 0x2 +#define TYPE_ANY (TYPE_FILE | TYPE_DIR) + +/** + * fat_itr_resolve() - traverse directory structure to resolve the + * requested path. + * + * Traverse directory structure to the requested path. If the specified + * path is to a directory, this will descend into the directory and + * leave it iterator at the start of the directory. If the path is to a + * file, it will leave the iterator in the parent directory with current + * cursor at file's entry in the directory. + * + * @itr: iterator initialized to root + * @path: the requested path + * @type: bitmask of allowable file types + * @return 0 on success or -errno + */ +static int fat_itr_resolve(fat_itr *itr, const char *path, unsigned type) +{ + const char *next; + + /* chomp any extra leading slashes: */ + while (path[0] && ISDIRDELIM(path[0])) + path++; + + /* are we at the end? */ + if (strlen(path) == 0) { + if (!(type & TYPE_DIR)) + return -ENOENT; + return 0; + } + + /* find length of next path entry: */ + next = path; + while (next[0] && !ISDIRDELIM(next[0])) + next++; + + while (fat_itr_next(itr)) { + int match = 0; + unsigned n = max(strlen(itr->name), (size_t)(next - path)); + + /* check both long and short name: */ + if (!strncasecmp(path, itr->name, n)) + match = 1; + else if (itr->name != itr->s_name && + !strncasecmp(path, itr->s_name, n)) + match = 1; + + if (!match) + continue; + + if (fat_itr_isdir(itr)) { + /* recurse into directory: */ + fat_itr_child(itr, itr); + return fat_itr_resolve(itr, next, type); + } else if (next[0]) { + /* + * If next is not empty then we have a case + * like: /path/to/realfile/nonsense + */ + debug("bad trailing path: %s\n", next); + return -ENOENT; + } else if (!(type & TYPE_FILE)) { + return -ENOTDIR; + } else { + return 0; + } + } + + return -ENOENT; +} + int do_fat_read(const char *filename, void *buffer, loff_t maxsize, int dols, loff_t *actread) { -- cgit v1.2.3