fs/namei.c: Add hashlen_string() function

We'd like to make more use of the highly-optimized dcache hash functions
throughout the kernel, rather than have every subsystem create its own,
and a function that hashes basic null-terminated strings is required
for that.

(The name is to emphasize that it returns both hash and length.)

It's actually useful in the dcache itself, specifically d_alloc_name().
Other uses in the next patch.

full_name_hash() is also tweaked to make it more generally useful:
1) Take a "char *" rather than "unsigned char *" argument, to
   be consistent with hash_name().
2) Handle zero-length inputs.  If we want more callers, we don't want
   to make them worry about corner cases.

Signed-off-by: George Spelvin <linux@sciencehorizons.net>

3 files changed, 53 insertions, 9 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index d5ecc6e477da..19b751806789 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1653,8 +1653,7 @@ struct dentry *d_alloc_name(struct dentry *parent, const char *name)
         struct qstr q;
 
         q.name = name;
-        q.len = strlen(name);
-        q.hash = full_name_hash(q.name, q.len);
+        q.hash_len = hashlen_string(name);
         return d_alloc(parent, &q);
 }
 EXPORT_SYMBOL(d_alloc_name);
diff --git a/fs/namei.c b/fs/namei.c
index 42f8ca038254..dd98d43a54f8 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1822,19 +1822,20 @@ static inline unsigned long mix_hash(unsigned long hash)
 
 #endif
 
-unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+/* Return the hash of a string of known length */
+unsigned int full_name_hash(const char *name, unsigned int len)
 {
         unsigned long a, hash = 0;
 
         for (;;) {
+                if (!len)
+                        goto done;
                 a = load_unaligned_zeropad(name);
                 if (len < sizeof(unsigned long))
                         break;
                 hash = mix_hash(hash + a);
                 name += sizeof(unsigned long);
                 len -= sizeof(unsigned long);
-                if (!len)
-                        goto done;
         }
         hash += a & bytemask_from_count(len);
 done:
@@ -1842,6 +1843,29 @@ done:
 }
 EXPORT_SYMBOL(full_name_hash);
 
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+u64 hashlen_string(const char *name)
+{
+        unsigned long a, adata, mask, hash, len;
+        const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
+
+        hash = a = 0;
+        len = -sizeof(unsigned long);
+        do {
+                hash = mix_hash(hash + a);
+                len += sizeof(unsigned long);
+                a = load_unaligned_zeropad(name+len);
+        } while (!has_zero(a, &adata, &constants));
+
+        adata = prep_zero_mask(a, adata, &constants);
+        mask = create_zero_mask(adata);
+        hash += a & zero_bytemask(mask);
+        len += find_zero(mask);
+
+        return hashlen_create(fold_hash(hash), len);
+}
+EXPORT_SYMBOL(hashlen_string);
+
 /*
  * Calculate the length and hash of the path component, and
  * return the "hash_len" as the result.
@@ -1872,15 +1896,32 @@ static inline u64 hash_name(const char *name)
 
 #else
 
-unsigned int full_name_hash(const unsigned char *name, unsigned int len)
+/* Return the hash of a string of known length */
+unsigned int full_name_hash(const char *name, unsigned int len)
 {
         unsigned long hash = init_name_hash();
         while (len--)
-                hash = partial_name_hash(*name++, hash);
+                hash = partial_name_hash((unsigned char)*name++, hash);
         return end_name_hash(hash);
 }
 EXPORT_SYMBOL(full_name_hash);
 
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+u64 hash_string(const char *name)
+{
+        unsigned long hash = init_name_hash();
+        unsigned long len = 0, c;
+
+        c = (unsigned char)*name;
+        do {
+                len++;
+                hash = partial_name_hash(c, hash);
+                c = (unsigned char)name[len];
+        } while (c);
+        return hashlen_create(end_name_hash(hash), len);
+}
+EXPORT_SYMBOL(hash_string);
+
 /*
  * We know there's a real path component here of at least
  * one character.
diff --git a/include/linux/stringhash.h b/include/linux/stringhash.h
index 2eaaaf6d2776..451771d9b9c0 100644
--- a/include/linux/stringhash.h
+++ b/include/linux/stringhash.h
@@ -1,7 +1,8 @@
 #ifndef __LINUX_STRINGHASH_H
 #define __LINUX_STRINGHASH_H
 
-#include <linux/types.h>
+#include <linux/compiler.h>     /* For __pure */
+#include <linux/types.h>        /* For u32, u64 */
 
 /*
  * Routines for hashing strings of bytes to a 32-bit hash value.
@@ -59,7 +60,7 @@ static inline unsigned long end_name_hash(unsigned long hash)
  *
  * If not set, this falls back to a wrapper around the preceding.
  */
-extern unsigned int full_name_hash(const unsigned char *, unsigned int);
+extern unsigned int __pure full_name_hash(const char *, unsigned int);
 
 /*
  * A hash_len is a u64 with the hash of a string in the low
@@ -69,4 +70,7 @@ extern unsigned int full_name_hash(const unsigned char *, unsigned int);
 #define hashlen_len(hashlen)  ((u32)((hashlen) >> 32))
 #define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash))
 
+/* Return the "hash_len" (hash and length) of a null-terminated string */
+extern u64 __pure hashlen_string(const char *name);
+
 #endif  /* __LINUX_STRINGHASH_H */