[nginx] Allowed up to two EBUSY errors from sendfile().

[Maxim Dounin]

details:   http://hg.nginx.org/nginx/rev/d39a69427056
branches:  
changeset: 5498:d39a69427056
user:      Maxim Dounin <mdounin at mdounin.ru>
date:      Sat Jan 04 03:31:58 2014 +0400
description:
Allowed up to two EBUSY errors from sendfile().

Fallback to synchronous sendfile() now only done on 3rd EBUSY without
any progress in a row.  Not falling back is believed to be better
in case of occasional EBUSY, though protection is still needed to
make sure there will be no infinite loop.

diffstat:

 src/core/ngx_connection.h              |  1 +
 src/http/ngx_http_copy_filter_module.c |  6 ++++--
 2 files changed, 5 insertions(+), 2 deletions(-)

diffs (32 lines):

diff --git a/src/core/ngx_connection.h b/src/core/ngx_connection.h
--- a/src/core/ngx_connection.h
+++ b/src/core/ngx_connection.h
@@ -177,6 +177,7 @@ struct ngx_connection_s {
 
 #if (NGX_HAVE_AIO_SENDFILE)
     unsigned            aio_sendfile:1;
+    unsigned            busy_count:2;
     ngx_buf_t          *busy_sendfile;
 #endif
 
diff --git a/src/http/ngx_http_copy_filter_module.c b/src/http/ngx_http_copy_filter_module.c
--- a/src/http/ngx_http_copy_filter_module.c
+++ b/src/http/ngx_http_copy_filter_module.c
@@ -169,13 +169,15 @@ ngx_http_copy_filter(ngx_http_request_t 
             offset = c->busy_sendfile->file_pos;
 
             if (file->aio) {
-                c->aio_sendfile = (offset != file->aio->last_offset);
+                c->busy_count = (offset == file->aio->last_offset) ?
+                                c->busy_count + 1 : 0;
                 file->aio->last_offset = offset;
 
-                if (c->aio_sendfile == 0) {
+                if (c->busy_count > 2) {
                     ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                                   "sendfile(%V) returned busy again",
                                   &file->name);
+                    c->aio_sendfile = 0;
                 }
             }