Define the functions and data structures to use as a name formatting
cache for msdos, using the generic Linux hashtable.
Signed-off-by: Caleb D.S. Brzezinski <calebdsb@xxxxxxxxxxxxxx>
---
fs/fat/namei_msdos.c | 96 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 96 insertions(+)
diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index efba301d6..7561674b1 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -9,12 +9,108 @@
#include <linux/module.h>
#include <linux/iversion.h>
+#include <linux/types.h>
+#include <linux/hashtable.h>
+#include <linux/slab.h>
+#include <linux/mutex.h>
#include "fat.h"
/* Characters that are undesirable in an MS-DOS file name */
static unsigned char bad_chars[] = "*?<>|\"";
static unsigned char bad_if_strict[] = "+=,; ";
+
+/**
+ * struct msdos_name_node - A formatted filename cache node
+ * @fname: the formatted filename
+ * @gc: a use counter for removing non-frequently used names
+ * @hash: the key for the item in the hash table
+ * @h_list: the list to the next set of values in this node's bucket
+ */
+struct msdos_name_node {
+ u16 gc;
+ char fname[9];
+ u64 hash;
+ struct hlist_node h_list;
+};
+
+DEFINE_HASHTABLE(msdos_ncache, 6);
+DEFINE_MUTEX(msdos_ncache_mutex); /* protect the name cache */
+
+/**
+ * msdos_fname_hash() - quickly "hash" an msdos filename
+ * @name: the name to hash, assumed to be a maximum of eight characters
+ *
+ * Bitwise-or the characters in an msdos filename into a simple "hash" that can
+ * be used as a fast hash for an msdos filename.
+ */
+static u64 msdos_fname_hash(const unsigned char *name)
+{
+ u64 res = 0;
+ short i;
+
+ for (i = 0; i < 8 && name[i] != '\0'; i++)
+ res |= (u64)(name[i] << (8 * i));
+
+ return res;
+}
+
+/**
+ * find_fname_in_cache() - retrieve a filename from the cache given a hash
+ * @out: the result buffer for the filename
+ * @ihash: the hash to check for
+ */
+static bool find_fname_in_cache(char *out, u64 ihash)
+{
+ struct msdos_name_node *node;
+ bool found = false;
+
+ mutex_lock(&msdos_ncache_mutex);
+ hash_for_each_possible(msdos_ncache, node, h_list, ihash) {
+ if (node->hash == ihash) {
+ strscpy(out, node->fname, 9);
+ found = true;
+ node->gc++;
+ goto out;
+ }
+ }
+
+out:
+ mutex_unlock(&msdos_ncache_mutex);
+ return found;
+}
+
+/**
+ * drop_fname_from_cache() - delete and free a filename from the hash entry
+ * @ihash: the hash to remove from the cache
+ */
+static void drop_fname_from_cache(u64 ihash)
+{
+ struct msdos_name_node *node, *gc;
+
+ gc = NULL;
+
+ mutex_lock(&msdos_ncache_mutex);
+ hash_for_each_possible(msdos_ncache, node, h_list, ihash) {
+ if (unlikely(gc)) {
+ hash_del(&gc->h_list);
+ kfree(gc);
+ gc = NULL;
+ }
+ if (node->hash == ihash) {
+ hash_del(&node->h_list);
+ kfree(node);
+ goto out;
+ }
+ /* if we don't find it, collect unused nodes until we do */
+ if (node->gc < 4)
+ gc = node;
+ }
+
+out:
+ mutex_unlock(&msdos_ncache_mutex);
+}
+
/***** Formats an MS-DOS file name. Rejects invalid names. */
static int msdos_format_name(const unsigned char *name, int len,
unsigned char *res, struct fat_mount_options *opts)
base-commit: 85a90500f9a1717c4e142ce92e6c1cb1a339ec78
--
2.32.0
