Copy filter: fixed sendfile aio handlers to set ctx->aio.

Sendfile handlers (aio preload and thread handler) are called within
ctx->output_filter() in ngx_output_chain(), and hence ctx->aio cannot
be set directly in ngx_output_chain().  Meanwhile, it must be set to
make sure loop within ngx_output_chain() will be properly terminated.

There are no known cases that trigger the problem, though in theory
something like aio + sub filter (something that needs body in memory,
and can also free some memory buffers) + sendfile can result in
"task already active" and "second aio post" alerts.

The fix is to set ctx->aio in ngx_http_copy_aio_sendfile_preload()
and ngx_http_copy_thread_handler().

For consistency, ctx->aio is no longer set explicitly in
ngx_output_chain_copy_buf(), as it's now done in
ngx_http_copy_thread_handler().

src/core/ngx_output_chain.c

diff --git a/src/core/ngx_output_chain.c b/src/core/ngx_output_chain.c
index 252359a..b8361dc 100644
--- a/src/core/ngx_output_chain.c
+++ b/src/core/ngx_output_chain.c
@@ -581,7 +581,6 @@
             n = ngx_thread_read(&ctx->thread_task, src->file, dst->pos,
                                 (size_t) size, src->file_pos, ctx->pool);
             if (n == NGX_AGAIN) {
-                ctx->aio = 1;
                 return NGX_AGAIN;
             }
 

src/http/ngx_http_copy_filter_module.c

diff --git a/src/http/ngx_http_copy_filter_module.c b/src/http/ngx_http_copy_filter_module.c
index c6d03ee..c696fb6 100644
--- a/src/http/ngx_http_copy_filter_module.c
+++ b/src/http/ngx_http_copy_filter_module.c
@@ -204,10 +204,11 @@
 static ssize_t
 ngx_http_copy_aio_sendfile_preload(ngx_buf_t *file)
 {
-    ssize_t              n;
-    static u_char        buf[1];
-    ngx_event_aio_t     *aio;
-    ngx_http_request_t  *r;
+    ssize_t                  n;
+    static u_char            buf[1];
+    ngx_event_aio_t         *aio;
+    ngx_http_request_t      *r;
+    ngx_output_chain_ctx_t  *ctx;
 
     n = ngx_file_aio_read(file->file, buf, 1, file->file_pos, NULL);
 
@@ -218,6 +219,9 @@
         r = aio->data;
         r->main->blocked++;
         r->aio = 1;
+
+        ctx = ngx_http_get_module_ctx(r, ngx_http_copy_filter_module);
+        ctx->aio = 1;
     }
 
     return n;
@@ -252,6 +256,7 @@
     ngx_str_t                  name;
     ngx_thread_pool_t         *tp;
     ngx_http_request_t        *r;
+    ngx_output_chain_ctx_t    *ctx;
     ngx_http_core_loc_conf_t  *clcf;
 
     r = file->thread_ctx;
@@ -285,6 +290,9 @@
     r->main->blocked++;
     r->aio = 1;
 
+    ctx = ngx_http_get_module_ctx(r, ngx_http_copy_filter_module);
+    ctx->aio = 1;
+
     return NGX_OK;
 }