[PATCH v6 4/5] smb/client: use bsearch() to find target in smb2_error_map_table

[chenxiaosong.chenxiaosong@linux.dev]

From: ChenXiaoSong <chenxiaosong@kylinos.cn>

The smb2_error_map_table array currently has 1740 elements. When searching
for the last element, the original loop-based search method requires 1740
comparisons, while binary search algorithm requires only 10 comparisons.

Suggested-by: David Howells <dhowells@redhat.com>
Signed-off-by: ChenXiaoSong <chenxiaosong@kylinos.cn>
---
 fs/smb/client/smb2maperror.c | 46 +++++++++++++++++++++++++++---------
 1 file changed, 35 insertions(+), 11 deletions(-)

diff --git a/fs/smb/client/smb2maperror.c b/fs/smb/client/smb2maperror.c
index 3731e32c22a3..b0241e6adbb6 100644
--- a/fs/smb/client/smb2maperror.c
+++ b/fs/smb/client/smb2maperror.c
@@ -27,13 +27,38 @@ static const struct status_to_posix_error smb2_error_map_table[] = {
 #include "smb2_mapping_table.c"
 };
 
+static __always_inline int cmp_smb2_status(const void *_a, const void *_b)
+{
+	const struct status_to_posix_error *a = _a, *b = _b;
+
+	if (a->smb2_status < b->smb2_status)
+		return -1;
+	if (a->smb2_status > b->smb2_status)
+		return 1;
+	return 0;
+}
+
+static struct status_to_posix_error *smb2_get_err_map(__le32 smb2_status)
+{
+	struct status_to_posix_error *err_map, key;
+
+	key = (struct status_to_posix_error) {
+		.smb2_status = smb2_status,
+	};
+	err_map = __inline_bsearch(&key, smb2_error_map_table,
+				   ARRAY_SIZE(smb2_error_map_table),
+				   sizeof(struct status_to_posix_error),
+				   cmp_smb2_status);
+	return err_map;
+}
+
 int
 map_smb2_to_linux_error(char *buf, bool log_err)
 {
 	struct smb2_hdr *shdr = (struct smb2_hdr *)buf;
-	unsigned int i;
 	int rc = -EIO;
 	__le32 smb2err = shdr->Status;
+	struct status_to_posix_error *err_map;
 
 	if (smb2err == 0) {
 		trace_smb3_cmd_done(le32_to_cpu(shdr->Id.SyncId.TreeId),
@@ -47,17 +72,16 @@ map_smb2_to_linux_error(char *buf, bool log_err)
 		   (smb2err != STATUS_END_OF_FILE)) ||
 		  (cifsFYI & CIFS_RC);
 
-	for (i = 0; i < sizeof(smb2_error_map_table) /
-			sizeof(struct status_to_posix_error); i++) {
-		if (smb2_error_map_table[i].smb2_status == smb2err) {
-			if (log_err)
-				pr_notice("Status code returned 0x%08x %s\n", smb2err,
-					  smb2_error_map_table[i].status_string);
-			rc = smb2_error_map_table[i].posix_error;
-			break;
-		}
-	}
+	err_map = smb2_get_err_map(smb2err);
+	if (!err_map)
+		goto out;
+
+	rc = err_map->posix_error;
+	if (log_err)
+		pr_notice("Status code returned 0x%08x %s\n", smb2err,
+			  err_map->status_string);
 
+out:
 	/* on error mapping not found  - return EIO */
 
 	cifs_dbg(FYI, "Mapping SMB2 status code 0x%08x to POSIX err %d\n",
-- 
2.43.0