[U-Boot] [PATCH v3 2/9] fs/fat: introduce new director iterators

Rob Clark
2017-09-09T17:15:53Z

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Untangle directory traversal into a simple iterator, to replace the
existing multi-purpose do_fat_read_at() + get_dentfromdir().

Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Łukasz Majewski <lukma@denx.de>
---
fs/fat/fat.c | 356 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
include/fat.h | 7 ++
2 files changed, 360 insertions(+), 3 deletions(-)

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)
{
diff --git a/include/fat.h b/include/fat.h
index b671ee8f81..21bb6666cf 100644
--- a/include/fat.h
+++ b/include/fat.h
@@ -175,8 +175,15 @@ typedef struct {
int data_begin; /* The sector of the first cluster, can be negative */
int fatbufnum; /* Used by get_fatent, init to -1 */
int rootdir_size; /* Size of root dir for non-FAT32 */
+ __u32 root_cluster; /* First cluster of root dir for FAT32 */
} fsdata;

+/* TODO clean up places that are open-coding this: */
+static inline u32 clust_to_sect(fsdata *fsdata, u32 clust)
+{
+ return fsdata->data_begin + clust * fsdata->clust_size;
+}
+
typedef int (file_detectfs_func)(void);
typedef int (file_ls_func)(const char *dir);
typedef int (file_read_func)(const char *filename, void *buffer,
--
2.13.5