PHP: optimization to avoid surplus chdir(2) calls.

For each request, the worker calls the php_execute_script function
from libphp that changes to the script directory before doing its
work and then restores the process directory before returning.  The
chdir(2) calls it performs are unnecessary in Unit design.  In simple
benchmarks, profiling shows that the chdir syscall code path (syscall,
FS walk, etc.) is where the CPU spends most of its time.

PHP SAPI semantics requires the script to be run from the script
directory.  In Unit's PHP implementation, we have two use cases:

- script
- arbitrary path

The "script" configuration doesn't have much need for a working
directory change: it can be changed once at module initialization.
The module needs to chdir again only if the user's PHP script also
calls chdir to switch to another directory during execution.

If "script" is not used in Unit configuration, we must ensure the
script is run from its directory (thus calling chdir before exec),
but there's no need to restore the working directory later.

Our implementation disables mandatory chdir calls with the SAPI
option SAPI_OPTION_NO_CHDIR, instead calling chdir only when needed.

To detect the user's calls to chdir, a simple "unit" extension is
added that hooks the built-in chdir() PHP call.

1 files changed, 299 insertions, 99 deletions

diff --git a/src/nxt_php_sapi.c b/src/nxt_php_sapi.c
index 917bc1c9..3702c371 100644
--- a/src/nxt_php_sapi.c
+++ b/src/nxt_php_sapi.c
@@ -29,7 +29,17 @@
 #define NXT_PHP7 1
 #endif
 
-typedef struct nxt_php_run_ctx_s  nxt_php_run_ctx_t;
+typedef struct {
+    char                     *cookie;
+    nxt_str_t                path_info;
+    nxt_str_t                script_name;
+    nxt_str_t                script_filename;
+    nxt_str_t                script_dirname;
+    nxt_unit_request_info_t  *req;
+
+    uint8_t                  chdir;  /* 1 bit */
+} nxt_php_run_ctx_t;
+
 
 #ifdef NXT_PHP7
 typedef int (*nxt_php_disable_t)(char *p, size_t size);
@@ -37,14 +47,24 @@ typedef int (*nxt_php_disable_t)(char *p, size_t size);
 typedef int (*nxt_php_disable_t)(char *p, uint TSRMLS_DC);
 #endif
 
+#if PHP_VERSION_ID < 70200
+typedef void (*zif_handler)(INTERNAL_FUNCTION_PARAMETERS);
+#endif
+
 
 static nxt_int_t nxt_php_init(nxt_task_t *task, nxt_common_app_conf_t *conf);
 
 static void nxt_php_str_trim_trail(nxt_str_t *str, u_char t);
 static void nxt_php_str_trim_lead(nxt_str_t *str, u_char t);
+static nxt_int_t nxt_php_dirname(const nxt_str_t *file, nxt_str_t *dir);
 nxt_inline u_char *nxt_realpath(const void *c);
+nxt_inline void nxt_php_vcwd_chdir(nxt_unit_request_info_t *req,
+    const nxt_str_t *dirname);
 
-static void nxt_php_request_handler(nxt_unit_request_info_t *req);
+static void nxt_php_script_request_handler(nxt_unit_request_info_t *req);
+static void nxt_php_path_request_handler(nxt_unit_request_info_t *req);
+static nxt_int_t nxt_php_request_init(nxt_php_run_ctx_t *ctx,
+    nxt_unit_request_t *r);
 
 static int nxt_php_startup(sapi_module_struct *sapi_module);
 static void nxt_php_set_options(nxt_task_t *task, nxt_conf_value_t *options,
@@ -54,6 +74,8 @@ static nxt_int_t nxt_php_alter_option(nxt_str_t *name, nxt_str_t *value,
 static void nxt_php_disable(nxt_task_t *task, const char *type,
     nxt_str_t *value, char **ptr, nxt_php_disable_t disable);
 static int nxt_php_send_headers(sapi_headers_struct *sapi_headers TSRMLS_DC);
+static void *nxt_php_hash_str_find_ptr(const HashTable *ht,
+    const nxt_str_t *str);
 static char *nxt_php_read_cookies(TSRMLS_D);
 static void nxt_php_set_sptr(nxt_unit_request_info_t *req, const char *name,
     nxt_unit_sptr_t *v, uint32_t len, zval *track_vars_array TSRMLS_DC);
@@ -78,6 +100,55 @@ static int nxt_php_read_post(char *buffer, uint count_bytes TSRMLS_DC);
 #endif
 
 
+PHP_MINIT_FUNCTION(nxt_php_ext);
+ZEND_NAMED_FUNCTION(nxt_php_chdir);
+
+zif_handler  nxt_php_chdir_handler;
+
+
+static zend_module_entry  nxt_php_unit_module = {
+    STANDARD_MODULE_HEADER,
+    "unit",
+    NULL,                        /* function table */
+    PHP_MINIT(nxt_php_ext),      /* initialization */
+    NULL,                        /* shutdown */
+    NULL,                        /* request initialization */
+    NULL,                        /* request shutdown */
+    NULL,                        /* information */
+    NXT_VERSION,
+    STANDARD_MODULE_PROPERTIES
+};
+
+
+PHP_MINIT_FUNCTION(nxt_php_ext)
+{
+    zend_function  *func;
+
+    static const nxt_str_t  chdir = nxt_string("chdir");
+
+    func = nxt_php_hash_str_find_ptr(CG(function_table), &chdir);
+    if (nxt_slow_path(func == NULL)) {
+        return FAILURE;
+    }
+
+    nxt_php_chdir_handler = func->internal_function.handler;
+    func->internal_function.handler = nxt_php_chdir;
+
+    return SUCCESS;
+}
+
+
+ZEND_NAMED_FUNCTION(nxt_php_chdir)
+{
+    nxt_php_run_ctx_t  *ctx;
+
+    ctx = SG(server_context);
+    ctx->chdir = 1;
+
+    nxt_php_chdir_handler(INTERNAL_FUNCTION_PARAM_PASSTHRU);
+}
+
+
 static sapi_module_struct  nxt_php_sapi_module =
 {
     (char *) "cli-server",
@@ -139,17 +210,9 @@ static sapi_module_struct  nxt_php_sapi_module =
 };
 
 
-struct nxt_php_run_ctx_s {
-    char                       *cookie;
-    nxt_str_t                  path_info;
-    nxt_str_t                  script_name;
-    nxt_str_t                  script_filename;
-    nxt_unit_request_info_t    *req;
-};
-
-
 static nxt_str_t nxt_php_root;
 static nxt_str_t nxt_php_script_name;
+static nxt_str_t nxt_php_script_dirname;
 static nxt_str_t nxt_php_script_filename;
 static nxt_str_t nxt_php_index = nxt_string("index.php");
 
@@ -180,7 +243,9 @@ nxt_php_init(nxt_task_t *task, nxt_common_app_conf_t *conf)
 {
     u_char              *p, *tmp;
     nxt_str_t           ini_path;
-    nxt_str_t           *root, *script_filename, *script_name, *index;
+    nxt_str_t           *root, *script_filename, *script_dirname, *script_name;
+    nxt_str_t           *index;
+    nxt_int_t           ret;
     nxt_port_t          *my_port, *main_port;
     nxt_runtime_t       *rt;
     nxt_unit_ctx_t      *unit_ctx;
@@ -203,6 +268,7 @@ nxt_php_init(nxt_task_t *task, nxt_common_app_conf_t *conf)
 
     root = &nxt_php_root;
     script_filename = &nxt_php_script_filename;
+    script_dirname = &nxt_php_script_dirname;
     script_name = &nxt_php_script_name;
     index = &nxt_php_index;
 
@@ -247,6 +313,11 @@ nxt_php_init(nxt_task_t *task, nxt_common_app_conf_t *conf)
             return NXT_ERROR;
         }
 
+        ret = nxt_php_dirname(script_filename, script_dirname);
+        if (nxt_slow_path(ret != NXT_OK)) {
+            return NXT_ERROR;
+        }
+
         script_name->length = c->script.length + 1;
         script_name->start = nxt_malloc(script_name->length);
         if (nxt_slow_path(script_name->start == NULL)) {
@@ -275,6 +346,22 @@ nxt_php_init(nxt_task_t *task, nxt_common_app_conf_t *conf)
         nxt_memcpy(index->start, c->index.start, c->index.length);
     }
 
+    nxt_memzero(&php_init, sizeof(nxt_unit_init_t));
+
+    if (nxt_php_script_filename.start != NULL) {
+        if (nxt_slow_path(chdir((char *) script_dirname->start) != 0)) {
+            nxt_alert(task, "failed to chdir(%V) %E", script_dirname,
+                      nxt_errno);
+
+            return NXT_ERROR;
+        }
+
+        php_init.callbacks.request_handler = nxt_php_script_request_handler;
+
+    } else {
+        php_init.callbacks.request_handler = nxt_php_path_request_handler;
+    }
+
 #ifdef ZTS
 
 #if PHP_VERSION_ID >= 70400
@@ -316,7 +403,10 @@ nxt_php_init(nxt_task_t *task, nxt_common_app_conf_t *conf)
         }
     }
 
-    nxt_php_startup(&nxt_php_sapi_module);
+    if (nxt_slow_path(nxt_php_startup(&nxt_php_sapi_module) == FAILURE)) {
+        nxt_alert(task, "failed to initialize SAPI module and extension");
+        return NXT_ERROR;
+    }
 
     if (c->options != NULL) {
         value = nxt_conf_get_object_member(c->options, &admin_str, NULL);
@@ -326,21 +416,20 @@ nxt_php_init(nxt_task_t *task, nxt_common_app_conf_t *conf)
         nxt_php_set_options(task, value, ZEND_INI_USER);
     }
 
-    nxt_memzero(&php_init, sizeof(nxt_unit_init_t));
-
     rt = task->thread->runtime;
 
     main_port = rt->port_by_type[NXT_PROCESS_MAIN];
     if (nxt_slow_path(main_port == NULL)) {
+        nxt_alert(task, "main process not found");
         return NXT_ERROR;
     }
 
     my_port = nxt_runtime_port_find(rt, nxt_pid, 0);
     if (nxt_slow_path(my_port == NULL)) {
+        nxt_alert(task, "my_port not found");
         return NXT_ERROR;
     }
 
-    php_init.callbacks.request_handler = nxt_php_request_handler;
     php_init.ready_port.id.pid = main_port->pid;
     php_init.ready_port.id.id = main_port->id;
     php_init.ready_port.out_fd = main_port->pair[1];
@@ -415,7 +504,7 @@ nxt_php_set_options(nxt_task_t *task, nxt_conf_value_t *options, int type)
 }
 
 
-#if (NXT_PHP7)
+#ifdef NXT_PHP7
 
 static nxt_int_t
 nxt_php_alter_option(nxt_str_t *name, nxt_str_t *value, int type)
@@ -423,10 +512,8 @@ nxt_php_alter_option(nxt_str_t *name, nxt_str_t *value, int type)
     zend_string     *zs;
     zend_ini_entry  *ini_entry;
 
-    ini_entry = zend_hash_str_find_ptr(EG(ini_directives),
-                                       (char *) name->start, name->length);
-
-    if (ini_entry == NULL) {
+    ini_entry = nxt_php_hash_str_find_ptr(EG(ini_directives), name);
+    if (nxt_slow_path(ini_entry == NULL)) {
         return NXT_ERROR;
     }
 
@@ -456,19 +543,9 @@ nxt_php_alter_option(nxt_str_t *name, nxt_str_t *value, int type)
 {
     char            *cstr;
     zend_ini_entry  *ini_entry;
-    char            buf[256];
 
-    if (nxt_slow_path(name->length >= sizeof(buf))) {
-        return NXT_ERROR;
-    }
-
-    nxt_memcpy(buf, name->start, name->length);
-    buf[name->length] = '\0';
-
-    if (zend_hash_find(EG(ini_directives), buf, name->length + 1,
-                       (void **) &ini_entry)
-        == FAILURE)
-    {
+    ini_entry = nxt_php_hash_str_find_ptr(EG(ini_directives), name);
+    if (nxt_slow_path(ini_entry == NULL)) {
         return NXT_ERROR;
     }
 
@@ -553,6 +630,33 @@ nxt_php_disable(nxt_task_t *task, const char *type, nxt_str_t *value,
 }
 
 
+static nxt_int_t
+nxt_php_dirname(const nxt_str_t *file, nxt_str_t *dir)
+{
+    size_t  length;
+
+    nxt_assert(file->length > 0 && file->start[0] == '/');
+
+    length = file->length;
+
+    while (file->start[length - 1] != '/') {
+        length--;
+    }
+
+    dir->length = length;
+    dir->start = nxt_malloc(length + 1);
+    if (nxt_slow_path(dir->start == NULL)) {
+        return NXT_ERROR;
+    }
+
+    nxt_memcpy(dir->start, file->start, length);
+
+    dir->start[length] = '\0';
+
+    return NXT_OK;
+}
+
+
 static void
 nxt_php_str_trim_trail(nxt_str_t *str, u_char t)
 {
@@ -582,12 +686,46 @@ nxt_realpath(const void *c)
 
 
 static void
-nxt_php_request_handler(nxt_unit_request_info_t *req)
+nxt_php_script_request_handler(nxt_unit_request_info_t *req)
+{
+    zend_file_handle   file_handle;
+    nxt_php_run_ctx_t  ctx;
+
+    nxt_memzero(&ctx, sizeof(ctx));
+
+    ctx.req = req;
+    ctx.script_filename = nxt_php_script_filename;
+    ctx.script_dirname = nxt_php_script_dirname;
+    ctx.script_name = nxt_php_script_name;
+
+    nxt_memzero(&file_handle, sizeof(file_handle));
+
+    file_handle.type = ZEND_HANDLE_FILENAME;
+    file_handle.filename = (char *) ctx.script_filename.start;
+
+    if (nxt_slow_path(nxt_php_request_init(&ctx, req->request) != NXT_OK)) {
+        nxt_unit_request_done(req, NXT_UNIT_ERROR);
+        return;
+    }
+
+    php_execute_script(&file_handle TSRMLS_CC);
+
+    if (ctx.chdir) {
+        nxt_php_vcwd_chdir(ctx.req, &nxt_php_script_dirname);
+    }
+
+    php_request_shutdown(NULL);
+
+    nxt_unit_request_done(req, NXT_UNIT_OK);
+}
+
+
+static void
+nxt_php_path_request_handler(nxt_unit_request_info_t *req)
 {
-    int                 rc;
     u_char              *p;
     nxt_str_t           path, script_name;
-    nxt_unit_field_t    *f;
+    nxt_int_t           ret;
     zend_file_handle    file_handle;
     nxt_php_run_ctx_t   run_ctx, *ctx;
     nxt_unit_request_t  *r;
@@ -602,59 +740,101 @@ nxt_php_request_handler(nxt_unit_request_info_t *req)
     path.length = r->path_length;
     path.start = nxt_unit_sptr_get(&r->path);
 
-    if (nxt_php_script_filename.start == NULL) {
-        nxt_str_null(&script_name);
-
-        ctx->path_info.start = (u_char *) strstr((char *) path.start, ".php/");
-        if (ctx->path_info.start != NULL) {
-            ctx->path_info.start += 4;
-            path.length = ctx->path_info.start - path.start;
+    nxt_str_null(&script_name);
 
-            ctx->path_info.length = r->path_length - path.length;
+    ctx->path_info.start = (u_char *) strstr((char *) path.start, ".php/");
+    if (ctx->path_info.start != NULL) {
+        ctx->path_info.start += 4;
+        path.length = ctx->path_info.start - path.start;
 
-        } else if (path.start[path.length - 1] == '/') {
-            script_name = nxt_php_index;
+        ctx->path_info.length = r->path_length - path.length;
 
-        } else {
-            if (nxt_slow_path(path.length < 4
-                              || nxt_memcmp(path.start + (path.length - 4),
-                                            ".php", 4)))
-            {
-                nxt_unit_request_done(req, NXT_UNIT_ERROR);
+    } else if (path.start[path.length - 1] == '/') {
+        script_name = nxt_php_index;
 
-                return;
-            }
-        }
-
-        ctx->script_filename.length = nxt_php_root.length + path.length
-                                      + script_name.length;
-        p = nxt_malloc(ctx->script_filename.length + 1);
-        if (nxt_slow_path(p == NULL)) {
+    } else {
+        if (nxt_slow_path(path.length < 4
+                          || nxt_memcmp(path.start + (path.length - 4),
+                                        ".php", 4)))
+        {
             nxt_unit_request_done(req, NXT_UNIT_ERROR);
 
             return;
         }
+    }
+
+    ctx->script_filename.length = nxt_php_root.length
+                                  + path.length
+                                  + script_name.length;
 
-        ctx->script_filename.start = p;
+    p = nxt_malloc(ctx->script_filename.length + 1);
+    if (nxt_slow_path(p == NULL)) {
+        nxt_unit_request_done(req, NXT_UNIT_ERROR);
 
-        ctx->script_name.length = path.length + script_name.length;
-        ctx->script_name.start = p + nxt_php_root.length;
+        return;
+    }
 
-        p = nxt_cpymem(p, nxt_php_root.start, nxt_php_root.length);
-        p = nxt_cpymem(p, path.start, path.length);
+    ctx->script_filename.start = p;
 
-        if (script_name.length > 0) {
-            p = nxt_cpymem(p, script_name.start, script_name.length);
-        }
+    ctx->script_name.length = path.length + script_name.length;
+    ctx->script_name.start = p + nxt_php_root.length;
 
-        *p = '\0';
+    p = nxt_cpymem(p, nxt_php_root.start, nxt_php_root.length);
+    p = nxt_cpymem(p, path.start, path.length);
 
-    } else {
-        ctx->script_filename = nxt_php_script_filename;
-        ctx->script_name = nxt_php_script_name;
+    if (script_name.length > 0) {
+        p = nxt_cpymem(p, script_name.start, script_name.length);
+    }
+
+    *p = '\0';
+
+    nxt_memzero(&file_handle, sizeof(file_handle));
+
+    file_handle.type = ZEND_HANDLE_FILENAME;
+    file_handle.filename = (char *) ctx->script_filename.start;
+
+    ret = nxt_php_dirname(&ctx->script_filename, &ctx->script_dirname);
+    if (nxt_slow_path(ret != NXT_OK)) {
+        nxt_unit_request_done(req, NXT_UNIT_ERROR);
+        nxt_free(ctx->script_filename.start);
+
+        return;
     }
 
+    if (nxt_slow_path(nxt_php_request_init(ctx, req->request) != NXT_OK)) {
+        nxt_unit_request_done(req, NXT_UNIT_ERROR);
+        goto cleanup;
+    }
+
+    nxt_php_vcwd_chdir(ctx->req, &ctx->script_dirname);
+
+    php_execute_script(&file_handle TSRMLS_CC);
+
+    php_request_shutdown(NULL);
+
+    nxt_unit_request_done(req, NXT_UNIT_OK);
+
+cleanup:
+
+    nxt_free(ctx->script_filename.start);
+    nxt_free(ctx->script_dirname.start);
+}
+
+
+static int
+nxt_php_startup(sapi_module_struct *sapi_module)
+{
+    return php_module_startup(sapi_module, &nxt_php_unit_module, 1);
+}
+
+
+static nxt_int_t
+nxt_php_request_init(nxt_php_run_ctx_t *ctx, nxt_unit_request_t *r)
+{
+    nxt_unit_field_t  *f;
+
     SG(server_context) = ctx;
+    SG(options) |= SAPI_OPTION_NO_CHDIR;
     SG(request_info).request_uri = nxt_unit_sptr_get(&r->target);
     SG(request_info).request_method = nxt_unit_sptr_get(&r->method);
 
@@ -680,55 +860,40 @@ nxt_php_request_handler(nxt_unit_request_info_t *req)
 
     SG(request_info).path_translated = NULL;
 
-    nxt_memzero(&file_handle, sizeof(file_handle));
-
-    file_handle.type = ZEND_HANDLE_FILENAME;
-    file_handle.filename = (char *) ctx->script_filename.start;
-
-    nxt_unit_req_debug(req, "handle.filename = '%s'",
+    nxt_unit_req_debug(ctx->req, "handle.filename = '%s'",
                        ctx->script_filename.start);
 
     if (nxt_php_script_filename.start != NULL) {
-        nxt_unit_req_debug(req, "run script %.*s in absolute mode",
+        nxt_unit_req_debug(ctx->req, "run script %.*s in absolute mode",
                            (int) nxt_php_script_filename.length,
                            (char *) nxt_php_script_filename.start);
 
     } else {
-        nxt_unit_req_debug(req, "run script %.*s",
+        nxt_unit_req_debug(ctx->req, "run script %.*s",
                            (int) ctx->script_filename.length,
                            (char *) ctx->script_filename.start);
     }
 
-#if (NXT_PHP7)
+#ifdef NXT_PHP7
     if (nxt_slow_path(php_request_startup() == FAILURE)) {
 #else
     if (nxt_slow_path(php_request_startup(TSRMLS_C) == FAILURE)) {
 #endif
-        nxt_unit_req_debug(req, "php_request_startup() failed");
-        rc = NXT_UNIT_ERROR;
+        nxt_unit_req_debug(ctx->req, "php_request_startup() failed");
 
-        goto fail;
+        return NXT_ERROR;
     }
 
-    rc = NXT_UNIT_OK;
-
-    php_execute_script(&file_handle TSRMLS_CC);
-    php_request_shutdown(NULL);
-
-fail:
-
-    nxt_unit_request_done(req, rc);
-
-    if (ctx->script_filename.start != nxt_php_script_filename.start) {
-        nxt_free(ctx->script_filename.start);
-    }
+    return NXT_OK;
 }
 
 
-static int
-nxt_php_startup(sapi_module_struct *sapi_module)
+nxt_inline void
+nxt_php_vcwd_chdir(nxt_unit_request_info_t *req, const nxt_str_t *dir)
 {
-    return php_module_startup(sapi_module, NULL, 0);
+    if (nxt_slow_path(VCWD_CHDIR((char *) dir->start) != 0)) {
+        nxt_unit_req_alert(req, "failed to VCWD_CHDIR(%V) %E", dir, nxt_errno);
+    }
 }
 
 
@@ -1005,6 +1170,41 @@ nxt_php_set_str(nxt_unit_request_info_t *req, const char *name,
 }
 
 
+#ifdef NXT_PHP7
+
+static void *
+nxt_php_hash_str_find_ptr(const HashTable *ht, const nxt_str_t *str)
+{
+    return zend_hash_str_find_ptr(ht, (const char *) str->start, str->length);
+}
+
+#else
+
+static void *
+nxt_php_hash_str_find_ptr(const HashTable *ht, const nxt_str_t *str)
+{
+    int   ret;
+    void  *entry;
+    char  buf[256];
+
+    if (nxt_slow_path(str->length >= (sizeof(buf) - 1))) {
+        return NULL;
+    }
+
+    nxt_memcpy(buf, str->start, str->length);
+    buf[str->length] = '\0';
+
+    ret = zend_hash_find(ht, buf, str->length + 1, &entry);
+    if (nxt_fast_path(ret == SUCCESS)) {
+        return entry;
+    }
+
+    return NULL;
+}
+
+#endif
+
+
 static void
 nxt_php_set_cstr(nxt_unit_request_info_t *req, const char *name,
     const char *cstr, uint32_t len, zval *track_vars_array TSRMLS_DC)