[nginx] Mp4: of.directio_off flag to avoid unneeded syscalls.

[Maxim Dounin]

details:   http://freenginx.org/hg/nginx/rev/268e0fb3a16c
branches:  
changeset: 9360:268e0fb3a16c
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Sun May 25 23:57:39 2025 +0300
description:
Mp4: of.directio_off flag to avoid unneeded syscalls.

When set, ngx_open_cached_file() won't try to enable directio on the file,
allowing the caller to do it itself, but will set is_directio flag in
ngx_open_file_info_t and in open file cache.  The fact that directio needs
to be enabled by the caller is signalled in the of.is_directio_off output
flag.

This approach makes it possible to avoid unneeded syscalls when directio
is enabled, yet the caller needs it disabled for some initial file
processing, such as in the mp4 module.

diffstat:

 src/core/ngx_open_file_cache.c         |   8 +++++++-
 src/core/ngx_open_file_cache.h         |   2 ++
 src/http/modules/ngx_http_mp4_module.c |  10 +++++-----
 3 files changed, 14 insertions(+), 6 deletions(-)

diffs (105 lines):

diff --git a/src/core/ngx_open_file_cache.c b/src/core/ngx_open_file_cache.c
--- a/src/core/ngx_open_file_cache.c
+++ b/src/core/ngx_open_file_cache.c
@@ -249,6 +249,7 @@ ngx_open_cached_file(ngx_open_file_cache
                 of->is_link = file->is_link;
                 of->is_exec = file->is_exec;
                 of->is_directio = file->is_directio;
+                of->is_directio_off = 0;
 
                 if (!file->is_dir) {
                     file->count++;
@@ -313,6 +314,7 @@ ngx_open_cached_file(ngx_open_file_cache
                 }
 
                 of->is_directio = file->is_directio;
+                of->is_directio_off = 0;
 
                 goto update;
             }
@@ -920,7 +922,11 @@ ngx_open_and_stat_file(ngx_str_t *name, 
         }
 
         if (of->directio <= ngx_file_size(&fi)) {
-            if (ngx_directio_on(fd) == NGX_FILE_ERROR) {
+            if (of->directio_off) {
+                of->is_directio = 1;
+                of->is_directio_off = 1;
+
+            } else if (ngx_directio_on(fd) == NGX_FILE_ERROR) {
                 ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
                               ngx_directio_on_n " \"%V\" failed", name);
 
diff --git a/src/core/ngx_open_file_cache.h b/src/core/ngx_open_file_cache.h
--- a/src/core/ngx_open_file_cache.h
+++ b/src/core/ngx_open_file_cache.h
@@ -42,12 +42,14 @@ typedef struct {
     unsigned                 log:1;
     unsigned                 errors:1;
     unsigned                 events:1;
+    unsigned                 directio_off:1;
 
     unsigned                 is_dir:1;
     unsigned                 is_file:1;
     unsigned                 is_link:1;
     unsigned                 is_exec:1;
     unsigned                 is_directio:1;
+    unsigned                 is_directio_off:1;
 } ngx_open_file_info_t;
 
 
diff --git a/src/http/modules/ngx_http_mp4_module.c b/src/http/modules/ngx_http_mp4_module.c
--- a/src/http/modules/ngx_http_mp4_module.c
+++ b/src/http/modules/ngx_http_mp4_module.c
@@ -479,7 +479,7 @@ ngx_http_mp4_handler(ngx_http_request_t 
     u_char                    *last;
     size_t                     root;
     ngx_int_t                  rc, start, end;
-    ngx_uint_t                 level, length, directio;
+    ngx_uint_t                 level, length;
     ngx_str_t                  path, value;
     ngx_log_t                 *log;
     ngx_buf_t                 *b;
@@ -520,6 +520,7 @@ ngx_http_mp4_handler(ngx_http_request_t 
 
     of.read_ahead = clcf->read_ahead;
     of.directio = clcf->directio;
+    of.directio_off = 1;
     of.valid = clcf->open_file_cache_valid;
     of.min_uses = clcf->open_file_cache_min_uses;
     of.errors = clcf->open_file_cache_errors;
@@ -579,7 +580,6 @@ ngx_http_mp4_handler(ngx_http_request_t 
 
     start = -1;
     length = 0;
-    directio = 0;
     r->headers_out.content_length_n = of.size;
     mp4 = NULL;
     b = NULL;
@@ -615,7 +615,7 @@ ngx_http_mp4_handler(ngx_http_request_t 
     if (start >= 0) {
         r->single_range = 1;
 
-        if (of.is_directio) {
+        if (of.is_directio && !of.is_directio_off) {
 
             /*
              * DIRECTIO is set on transfer only
@@ -627,7 +627,7 @@ ngx_http_mp4_handler(ngx_http_request_t 
                               ngx_directio_off_n " \"%s\" failed", path.data);
             }
 
-            directio = 1;
+            of.is_directio_off = 1;
         }
 
         mp4 = ngx_pcalloc(r->pool, sizeof(ngx_http_mp4_file_t));
@@ -673,7 +673,7 @@ ngx_http_mp4_handler(ngx_http_request_t 
 
     log->action = "sending mp4 to client";
 
-    if (directio) {
+    if (of.is_directio_off) {
 
         /* DIRECTIO was switched off, restore it */