s3: smbd: Remove a STAT/LSTAT call on the parent pathname in a hot code path.

This optimization uses the stored errno result from check_parent_exists()
which already did a STAT/LSTAT if needed.

Best viewed with 'git show -b'.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Richard Sharpe <realrichardsharpe@gmail.com>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Tue May 11 22:52:58 UTC 2021 on sn-devel-184

diff --git a/source3/smbd/filename.c b/source3/smbd/filename.c
index 6181afce8984f20021c7b5c4d99d9cc5d802b2e9..44a58a20c1ff737803379ebfd848bf01236f9f87 100644 (file)
--- a/source3/smbd/filename.c
+++ b/source3/smbd/filename.c
@@ -1174,6 +1174,8 @@ NTSTATUS unix_convert(TALLOC_CTX *mem_ctx,
                  state->smb_fname->base_name, state->dirpath, state->name);
 
        if (!state->name_has_wildcard) {
+               int parent_stat_errno = 0;
+
                /*
                 * stat the name - if it exists then we can add the stream back (if
                 * there was one) and be done!
@@ -1218,7 +1220,7 @@ NTSTATUS unix_convert(TALLOC_CTX *mem_ctx,
                                                state->smb_fname,
                                                &state->dirpath,
                                                &state->name,
-                                               NULL);
+                                               &parent_stat_errno);
                        errno = saved_errno;
                        if (!NT_STATUS_IS_OK(status)) {
                                goto fail;
@@ -1252,29 +1254,30 @@ NTSTATUS unix_convert(TALLOC_CTX *mem_ctx,
                                /*
                                 * Was it a missing last component ?
                                 * or a missing intermediate component ?
+                                *
+                                * Optimization.
+                                *
+                                * For this code path we can guarantee that
+                                * we have gone through check_parent_exists()
+                                * and it returned NT_STATUS_OK.
+                                *
+                                * Either there was no parent component (".")
+                                * parent_stat_errno == 0 and we have a missing
+                                * last component here.
+                                *
+                                * OR check_parent_exists() called STAT/LSTAT
+                                * and if it failed parent_stat_errno has been
+                                * set telling us if the parent existed or not.
+                                *
+                                * Either way we can avoid another STAT/LSTAT
+                                * system call on the parent here.
                                 */
-                               struct smb_filename *parent_fname = NULL;
-                               struct smb_filename *base_fname = NULL;
-                               bool ok;
-
-                               ok = parent_smb_fname(state->mem_ctx,
-                                                     state->smb_fname,
-                                                     &parent_fname,
-                                                     &base_fname);
-                               if (!ok) {
-                                       status = NT_STATUS_NO_MEMORY;
+                               if (parent_stat_errno == ENOTDIR ||
+                                               parent_stat_errno == ENOENT ||
+                                               parent_stat_errno == ELOOP) {
+                                       status = NT_STATUS_OBJECT_PATH_NOT_FOUND;
                                        goto fail;
                                }
-                               ret = vfs_stat(state->conn, parent_fname);
-                               TALLOC_FREE(parent_fname);
-                               if (ret == -1) {
-                                       if (errno == ENOTDIR ||
-                                                       errno == ENOENT ||
-                                                       errno == ELOOP) {
-                                               status = NT_STATUS_OBJECT_PATH_NOT_FOUND;
-                                               goto fail;
-                                       }
-                               }
 
                                /*
                                 * Missing last component is ok - new file.