ceph: replace local base64 helpers with lib/base64

Remove the ceph_base64_encode() and ceph_base64_decode() functions and
replace their usage with the generic base64_encode() and base64_decode()
helpers from lib/base64.

This eliminates the custom implementation in Ceph, reduces code
duplication, and relies on the shared Base64 code in lib. The helpers
preserve RFC 3501-compliant Base64 encoding without padding, so there are
no functional changes.

This change also improves performance: encoding is about 2.7x faster and
decoding achieves 43-52x speedups compared to the previous local
implementation.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Guan-Chun Wu <[e-mail]>
Reviewed-by: Kuan-Wei Chiu <[e-mail]>
Reviewed-by: Viacheslav Dubeyko <[e-mail]>
Cc: Keith Busch <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Sagi Grimberg <[e-mail]>
Cc: Xiubo Li <[e-mail]>
Cc: Ilya Dryomov <[e-mail]>
Cc: Eric Biggers <[e-mail]>
Cc: "Theodore Y. Ts'o" <[e-mail]>
Cc: Jaegeuk Kim <[e-mail]>
Cc: David Laight <[e-mail]>
Cc: Yu-Sheng Huang <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

fs/ceph/crypto.c

···
 #include "mds_client.h"
 #include "crypto.h"
 
-/*
- * The base64url encoding used by fscrypt includes the '_' character, which may
- * cause problems in snapshot names (which can not start with '_').  Thus, we
- * used the base64 encoding defined for IMAP mailbox names (RFC 3501) instead,
- * which replaces '-' and '_' by '+' and ','.
- */
-static const char base64_table[65] =
-	"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+,";
-
-int ceph_base64_encode(const u8 *src, int srclen, char *dst)
-{
-	u32 ac = 0;
-	int bits = 0;
-	int i;
-	char *cp = dst;
-
-	for (i = 0; i < srclen; i++) {
-		ac = (ac << 8) | src[i];
-		bits += 8;
-		do {
-			bits -= 6;
-			*cp++ = base64_table[(ac >> bits) & 0x3f];
-		} while (bits >= 6);
-	}
-	if (bits)
-		*cp++ = base64_table[(ac << (6 - bits)) & 0x3f];
-	return cp - dst;
-}
-
-int ceph_base64_decode(const char *src, int srclen, u8 *dst)
-{
-	u32 ac = 0;
-	int bits = 0;
-	int i;
-	u8 *bp = dst;
-
-	for (i = 0; i < srclen; i++) {
-		const char *p = strchr(base64_table, src[i]);
-
-		if (p == NULL || src[i] == 0)
-			return -1;
-		ac = (ac << 6) | (p - base64_table);
-		bits += 6;
-		if (bits >= 8) {
-			bits -= 8;
-			*bp++ = (u8)(ac >> bits);
-		}
-	}
-	if (ac & ((1 << bits) - 1))
-		return -1;
-	return bp - dst;
-}
-
 static int ceph_crypt_get_context(struct inode *inode, void *ctx, size_t len)
 {
 	struct ceph_inode_info *ci = ceph_inode(inode);
···
 	}
 
 	/* base64 encode the encrypted name */
-	elen = ceph_base64_encode(cryptbuf, len, p);
+	elen = base64_encode(cryptbuf, len, p, false, BASE64_IMAP);
 	doutc(cl, "base64-encoded ciphertext name = %.*s\n", elen, p);
 
 	/* To understand the 240 limit, see CEPH_NOHASH_NAME_MAX comments */
···
 			tname = &_tname;
 		}
 
-		declen = ceph_base64_decode(name, name_len, tname->name);
+		declen = base64_decode(name, name_len,
+				       tname->name, false, BASE64_IMAP);
 		if (declen <= 0) {
 			ret = -EIO;
 			goto out;
···
 
 	ret = fscrypt_fname_disk_to_usr(dir, 0, 0, &iname, oname);
 	if (!ret && (dir != fname->dir)) {
-		char tmp_buf[CEPH_BASE64_CHARS(NAME_MAX)];
+		char tmp_buf[BASE64_CHARS(NAME_MAX)];
 
 		name_len = snprintf(tmp_buf, sizeof(tmp_buf), "_%.*s_%ld",
 				    oname->len, oname->name, dir->i_ino);

fs/ceph/crypto.h

···
 
 #include <crypto/sha2.h>
 #include <linux/fscrypt.h>
+#include <linux/base64.h>
 
 #define CEPH_FSCRYPT_BLOCK_SHIFT   12
 #define CEPH_FSCRYPT_BLOCK_SIZE    (_AC(1, UL) << CEPH_FSCRYPT_BLOCK_SHIFT)
···
  * field).
  */
 #define CEPH_NOHASH_NAME_MAX (180 - SHA256_DIGEST_SIZE)
-
-#define CEPH_BASE64_CHARS(nbytes) DIV_ROUND_UP((nbytes) * 4, 3)
-
-int ceph_base64_encode(const u8 *src, int srclen, char *dst);
-int ceph_base64_decode(const char *src, int srclen, u8 *dst);
 
 void ceph_fscrypt_set_ops(struct super_block *sb);
 

fs/ceph/dir.c

···
 	if (err)
 		goto out;
 
-	req->r_path2 = kmalloc(CEPH_BASE64_CHARS(osd_link.len) + 1, GFP_KERNEL);
+	req->r_path2 = kmalloc(BASE64_CHARS(osd_link.len) + 1, GFP_KERNEL);
 	if (!req->r_path2) {
 		err = -ENOMEM;
 		goto out;
 	}
 
-	len = ceph_base64_encode(osd_link.name, osd_link.len, req->r_path2);
+	len = base64_encode(osd_link.name, osd_link.len,
+			    req->r_path2, false, BASE64_IMAP);
 	req->r_path2[len] = '\0';
 out:
 	fscrypt_fname_free_buffer(&osd_link);

fs/ceph/inode.c

···
 	if (!sym)
 		return -ENOMEM;
 
-	declen = ceph_base64_decode(encsym, enclen, sym);
+	declen = base64_decode(encsym, enclen, sym, false, BASE64_IMAP);
 	if (declen < 0) {
 		pr_err_client(cl,
 			"can't decode symlink (%d). Content: %.*s\n",