uniform ngx_directio_on/off() interface with other file functions

src/core/ngx_open_file_cache.c

diff --git a/src/core/ngx_open_file_cache.c b/src/core/ngx_open_file_cache.c
index aa87fd2..5f6e0b2 100644
--- a/src/core/ngx_open_file_cache.c
+++ b/src/core/ngx_open_file_cache.c
@@ -525,7 +525,7 @@
         of->fd = fd;
 
         if (of->directio <= ngx_file_size(&fi)) {
-            if (ngx_directio_on(fd) == -1) {
+            if (ngx_directio_on(fd) == NGX_FILE_ERROR) {
                 ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
                               ngx_directio_on_n " \"%s\" failed", name);
 

src/core/ngx_output_chain.c

diff --git a/src/core/ngx_output_chain.c b/src/core/ngx_output_chain.c
index 590da4f..3ff25ff 100644
--- a/src/core/ngx_output_chain.c
+++ b/src/core/ngx_output_chain.c
@@ -514,7 +514,7 @@
 #if (NGX_HAVE_ALIGNED_DIRECTIO)
 
         if (ctx->unaligned) {
-            if (ngx_directio_off(src->file->fd) == -1) {
+            if (ngx_directio_off(src->file->fd) == NGX_FILE_ERROR) {
                 ngx_log_error(NGX_LOG_ALERT, ctx->pool->log, ngx_errno,
                               ngx_directio_off_n " \"%s\" failed",
                               src->file->name.data);
@@ -550,7 +550,7 @@
 
             err = ngx_errno;
 
-            if (ngx_directio_on(src->file->fd) == -1) {
+            if (ngx_directio_on(src->file->fd) == NGX_FILE_ERROR) {
                 ngx_log_error(NGX_LOG_ALERT, ctx->pool->log, ngx_errno,
                               ngx_directio_on_n " \"%s\" failed",
                               src->file->name.data);

src/os/unix/ngx_files.c

diff --git a/src/os/unix/ngx_files.c b/src/os/unix/ngx_files.c
index d4bf043..2154bed 100644
--- a/src/os/unix/ngx_files.c
+++ b/src/os/unix/ngx_files.c
@@ -406,7 +406,7 @@
     flags = fcntl(fd, F_GETFL);
 
     if (flags == -1) {
-        return -1;
+        return NGX_FILE_ERROR;
     }
 
     return fcntl(fd, F_SETFL, flags | O_DIRECT);
@@ -421,7 +421,7 @@
     flags = fcntl(fd, F_GETFL);
 
     if (flags == -1) {
-        return -1;
+        return NGX_FILE_ERROR;
     }
 
     return fcntl(fd, F_SETFL, flags & ~O_DIRECT);

src/os/win32/ngx_files.c

diff --git a/src/os/win32/ngx_files.c b/src/os/win32/ngx_files.c
index bfbb98f..70cab2f 100644
--- a/src/os/win32/ngx_files.c
+++ b/src/os/win32/ngx_files.c
@@ -479,14 +479,14 @@
 ngx_int_t
 ngx_directio_on(ngx_fd_t fd)
 {
-    return 0;
+    return ~NGX_FILE_ERROR;
 }
 
 
 ngx_int_t
 ngx_directio_off(ngx_fd_t fd)
 {
-    return 0;
+    return ~NGX_FILE_ERROR;
 }