core/ngx_open_file_cache.c源文件分析
本节主要讲述一下nginx对静态文件的缓存相关操作。
1. nginx静态文件缓存
这里在介绍具体的源代码之前，我们首先简要介绍一下Nginx服务器中静态文件Cache的一个大体处理流程。事实上，整个nginx中只有两个地方会用到这种静态文件缓存：
-
ngx_http_core_module
-
ngx_http_log_module
nginx静态文件缓存中，可以存储如下信息：
-
打开的文件描述符、文件大小、修改时间
-
目录是否存在等信息
-
与文件查找相关的任何错误消息，例如
file not found、no read permission
注意： 如果要缓存错误信息的话，那么还需要单独启用 'open_file_cache_errors' 子令
其基本使用示例如下：
open_file_cache max=64 inactive=30d; open_file_cache_min_uses 8; open_file_cache_valid 3m; open_file_cache_errors on;
上面 ‘max=64’ 表示设置缓冲文件的最大数目为64。超过此数目后，Nginx将按照LRU原则丢弃冷数据。‘inactive=30d’ 与 ‘open_file_cache_min_uses 8’ 表示如果在30天内某文件的访问次数低于8次，那就将它从缓存中删除。
‘open_file_cache_valid 3m’表示每3分钟检查一次缓存中的文件信息是否正确，如果不是则更新之。
1.1 原理介绍
这里我们主要介绍一下Linux下Nginx的静态文件缓存的实现。对于BSD版本，由于其可以通过kqueue来监听文件改变的事件，因此其实现会有一个不同的做法，这里我们不对其做详细介绍。
在Linux下，Nginx并没有使用Inotify，而是每次都会判断文件的st_ino来得到文件是否被修改，不过这样会有个缺点就是如果你是使用open()，然后write()来修改文件的话，因为是属于修改同一个文件，因此st_ino是相同的，此时Nginx是无法感知到文件被修改了。因此要修改文件的话，最好使用先删除再覆盖的命令（比如cp命令)。
Nginx中的Cache只是cache文件句柄，因为静态文件的发送，一般来说，Nginx都是尽量使用sendfile()来进行发送的。因此只需要cache文件句柄就足够了。
所有的Cache对象包含在两个数据结构里面，整个机制最关键的也是这两个东西，一个是红黑树，另一个就是队列。其中红黑树是为了方便查找（能根据文件名迅速得到fd)，而队列是为了方便超时管理（按照读取顺序插入，在队列头的就是最近存取的文件），由于所有的句柄的超时时间都是一样的，因此每次只需要判断最后几个元素就够了，因为这个超时并不需要那么实时。如下画出cache存储结构的整体图景：
假如现在客户端的请求是GET test.html HTTP/1.1，则Nginx是这么处理的，如果test.html在cache中存在，则从cache中取得这个句柄，然后正常返回；如果test.html不存在，则是打开这个文件，然后插入到cache中。不过这里面有很多细节需要处理，比如超时，比如红黑树的插入等等。我们会在后面的章节来较为详细的介绍这些。
1.2 文件缓存更新周期
上面提到的配置文件中，若文件在30天内访问的次数低于8次，那么将会从缓存中丢弃。每3分钟做一次信息有效性监测，这里我们暂且把3分钟称为缓存更新周期。那在这3分钟之内文件发生变化了会怎样呢？
1） 文件被删除
由于nginx还持有原文件的fd，所以你删除此文件后，文件并不会真正消失，client还是能够通过原路径访问此文件。即便你删除后又新建了一个同名文件，在当前缓存更新周期内能访问到的还是原文件的内容。
2） 文件内容被修改
文件内容被修改可以分成两种情况：
- 文件大小不变或增大： 由于nginx缓存了文件的size，并且使用缓存中的size调用sendfile(2)，所以此种情况的后果是：
1. 从文件开始到原size字节中的变化可以被client看到； 2. 原size之后的内容不会被sendfile(2)发送，因此client看不到此部分内容；
- 文件大小减小： 此种情况下，由于同样的原因，nginx在HTTP Header中告诉client文件大小还是原来的尺寸，而sendfile(2)只能发送真正的文件数据，长度小于HTTP Header中设置的大小，所以client会等待到自己超时或者Nginx在epoll_wait超时后关闭连接。
1.3 如何设置Nginx静态缓存
我们在使用Nginx静态文件缓存时，可以考虑如下：
-
如果你的静态文件内容变化频繁并且对时效性要求较高，一般应该把 ‘open_file_cache_valid’ 设置的小一些，以便及时检测和更新；
-
如果变化相当不频繁的话， 就可以设置大一点。在变化后用reload nginx的方式来强制更新缓存；
-
对静态文件访问的error和access log不关心的话，可以关闭以提升效率。
3. 相关静态函数声明
/*
* Copyright (C) Igor Sysoev
* Copyright (C) Nginx, Inc.
*/
#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_event.h>
/*
* open file cache caches
* open file handles with stat() info;
* directories stat() info;
* files and directories errors: not found, access denied, etc.
*/
#define NGX_MIN_READ_AHEAD (128 * 1024)
//用于清除超时队列中的所有
static void ngx_open_file_cache_cleanup(void *data);
#if (NGX_HAVE_OPENAT)
//使用openat()来打开一个文件，因为openat()打开的文件并不能判定是不是链接文件，所以需要进一步判断
static ngx_fd_t ngx_openat_file_owner(ngx_fd_t at_fd, const u_char *name,
ngx_int_t mode, ngx_int_t create, ngx_int_t access, ngx_log_t *log);
#if (NGX_HAVE_O_PATH)
//使用O_PATH选项来打开一个文件或目录以获得相应的文件信息
static ngx_int_t ngx_file_o_path_info(ngx_fd_t fd, ngx_file_info_t *fi,
ngx_log_t *log);
#endif
#endif
//打开一个文件，主要是封装了普通打开方式与openat()
static ngx_fd_t ngx_open_file_wrapper(ngx_str_t *name,
ngx_open_file_info_t *of, ngx_int_t mode, ngx_int_t create,
ngx_int_t access, ngx_log_t *log);
//获取文件信息
static ngx_int_t ngx_file_info_wrapper(ngx_str_t *name,
ngx_open_file_info_t *of, ngx_file_info_t *fi, ngx_log_t *log);
//打开并stat一个文件
static ngx_int_t ngx_open_and_stat_file(ngx_str_t *name,
ngx_open_file_info_t *of, ngx_log_t *log);
//打开一个文件并添加相应的事件
static void ngx_open_file_add_event(ngx_open_file_cache_t *cache,
ngx_cached_open_file_t *file, ngx_open_file_info_t *of, ngx_log_t *log);
//清除一个打开的文件信息
static void ngx_open_file_cleanup(void *data);
//关闭缓存文件
static void ngx_close_cached_file(ngx_open_file_cache_t *cache,
ngx_cached_open_file_t *file, ngx_uint_t min_uses, ngx_log_t *log);
//删除关联在文件上的事件
static void ngx_open_file_del_event(ngx_cached_open_file_t *file);
//淘汰超时的、老旧的缓存文件
static void ngx_expire_old_cached_files(ngx_open_file_cache_t *cache,
ngx_uint_t n, ngx_log_t *log);
//将缓存文件信息插入到红黑树中
static void ngx_open_file_cache_rbtree_insert_value(ngx_rbtree_node_t *temp,
ngx_rbtree_node_t *node, ngx_rbtree_node_t *sentinel);
//从红黑树中查找文件
static ngx_cached_open_file_t *
ngx_open_file_lookup(ngx_open_file_cache_t *cache, ngx_str_t *name,
uint32_t hash);
//移除事件所关联的文件缓存信息
static void ngx_open_file_cache_remove(ngx_event_t *ev);这里nginx对打开文件的缓存，主要有三种类型：
1) 打开文件的句柄，以及该文件对应额stat()信息
2） 目录的stat()信息；
3） 与文件查找相关的任何错误消息，例如file not found、no read permission
4. 函数ngx_open_file_cache_init()
ngx_open_file_cache_t *
ngx_open_file_cache_init(ngx_pool_t *pool, ngx_uint_t max, time_t inactive)
{
ngx_pool_cleanup_t *cln;
ngx_open_file_cache_t *cache;
cache = ngx_palloc(pool, sizeof(ngx_open_file_cache_t));
if (cache == NULL) {
return NULL;
}
ngx_rbtree_init(&cache->rbtree, &cache->sentinel,
ngx_open_file_cache_rbtree_insert_value);
ngx_queue_init(&cache->expire_queue);
cache->current = 0;
cache->max = max;
cache->inactive = inactive;
cln = ngx_pool_cleanup_add(pool, 0);
if (cln == NULL) {
return NULL;
}
cln->handler = ngx_open_file_cache_cleanup;
cln->data = cache;
return cache;
}本函数较为简单，主要是初始化了ngx_open_file_cache_t数据结构，并将其加入到pool cleanup中，来让其自动的管理cache的回收工作。
5. 函数ngx_open_file_cache_cleanup()
static void
ngx_open_file_cache_cleanup(void *data)
{
ngx_open_file_cache_t *cache = data;
ngx_queue_t *q;
ngx_cached_open_file_t *file;
ngx_log_debug0(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
"open file cache cleanup");
for ( ;; ) {
if (ngx_queue_empty(&cache->expire_queue)) {
break;
}
q = ngx_queue_last(&cache->expire_queue);
file = ngx_queue_data(q, ngx_cached_open_file_t, queue);
ngx_queue_remove(q);
ngx_rbtree_delete(&cache->rbtree, &file->node);
cache->current--;
ngx_log_debug1(NGX_LOG_DEBUG_CORE, ngx_cycle->log, 0,
"delete cached open file: %s", file->name);
if (!file->err && !file->is_dir) {
file->close = 1;
file->count = 0;
ngx_close_cached_file(cache, file, 0, ngx_cycle->log);
} else {
ngx_free(file->name);
ngx_free(file);
}
}
if (cache->current) {
ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, 0,
"%ui items still left in open file cache",
cache->current);
}
if (cache->rbtree.root != cache->rbtree.sentinel) {
ngx_log_error(NGX_LOG_ALERT, ngx_cycle->log, 0,
"rbtree still is not empty in open file cache");
}
}本函数用于从超时队列及红黑树中删除相应的缓存文件数据。一般来说，把所有的缓存数据从超时队列中移除之后，cache->current的值就会为0，如果不为0，表示出现了相应的错误，这里我们也只是打印相应的错误日志消息。
6. 函数ngx_open_cached_file()
ngx_int_t
ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool)
{
time_t now;
uint32_t hash;
ngx_int_t rc;
ngx_file_info_t fi;
ngx_pool_cleanup_t *cln;
ngx_cached_open_file_t *file;
ngx_pool_cleanup_file_t *clnf;
ngx_open_file_cache_cleanup_t *ofcln;
of->fd = NGX_INVALID_FILE;
of->err = 0;
if (cache == NULL) {
if (of->test_only) {
if (ngx_file_info_wrapper(name, of, &fi, pool->log)
== NGX_FILE_ERROR)
{
return NGX_ERROR;
}
of->uniq = ngx_file_uniq(&fi);
of->mtime = ngx_file_mtime(&fi);
of->size = ngx_file_size(&fi);
of->fs_size = ngx_file_fs_size(&fi);
of->is_dir = ngx_is_dir(&fi);
of->is_file = ngx_is_file(&fi);
of->is_link = ngx_is_link(&fi);
of->is_exec = ngx_is_exec(&fi);
return NGX_OK;
}
cln = ngx_pool_cleanup_add(pool, sizeof(ngx_pool_cleanup_file_t));
if (cln == NULL) {
return NGX_ERROR;
}
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc == NGX_OK && !of->is_dir) {
cln->handler = ngx_pool_cleanup_file;
clnf = cln->data;
clnf->fd = of->fd;
clnf->name = name->data;
clnf->log = pool->log;
}
return rc;
}
cln = ngx_pool_cleanup_add(pool, sizeof(ngx_open_file_cache_cleanup_t));
if (cln == NULL) {
return NGX_ERROR;
}
now = ngx_time();
hash = ngx_crc32_long(name->data, name->len);
file = ngx_open_file_lookup(cache, name, hash);
if (file) {
file->uses++;
ngx_queue_remove(&file->queue);
if (file->fd == NGX_INVALID_FILE && file->err == 0 && !file->is_dir) {
/* file was not used often enough to keep open */
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc != NGX_OK && (of->err == 0 || !of->errors)) {
goto failed;
}
goto add_event;
}
if (file->use_event
|| (file->event == NULL
&& (of->uniq == 0 || of->uniq == file->uniq)
&& now - file->created < of->valid
#if (NGX_HAVE_OPENAT)
&& of->disable_symlinks == file->disable_symlinks
&& of->disable_symlinks_from == file->disable_symlinks_from
#endif
))
{
if (file->err == 0) {
of->fd = file->fd;
of->uniq = file->uniq;
of->mtime = file->mtime;
of->size = file->size;
of->is_dir = file->is_dir;
of->is_file = file->is_file;
of->is_link = file->is_link;
of->is_exec = file->is_exec;
of->is_directio = file->is_directio;
if (!file->is_dir) {
file->count++;
ngx_open_file_add_event(cache, file, of, pool->log);
}
} else {
of->err = file->err;
#if (NGX_HAVE_OPENAT)
of->failed = file->disable_symlinks ? ngx_openat_file_n
: ngx_open_file_n;
#else
of->failed = ngx_open_file_n;
#endif
}
goto found;
}
ngx_log_debug4(NGX_LOG_DEBUG_CORE, pool->log, 0,
"retest open file: %s, fd:%d, c:%d, e:%d",
file->name, file->fd, file->count, file->err);
if (file->is_dir) {
/*
* chances that directory became file are very small
* so test_dir flag allows to use a single syscall
* in ngx_file_info() instead of three syscalls
*/
of->test_dir = 1;
}
of->fd = file->fd;
of->uniq = file->uniq;
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc != NGX_OK && (of->err == 0 || !of->errors)) {
goto failed;
}
if (of->is_dir) {
if (file->is_dir || file->err) {
goto update;
}
/* file became directory */
} else if (of->err == 0) { /* file */
if (file->is_dir || file->err) {
goto add_event;
}
if (of->uniq == file->uniq) {
if (file->event) {
file->use_event = 1;
}
of->is_directio = file->is_directio;
goto update;
}
/* file was changed */
} else { /* error to cache */
if (file->err || file->is_dir) {
goto update;
}
/* file was removed, etc. */
}
if (file->count == 0) {
ngx_open_file_del_event(file);
if (ngx_close_file(file->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,
ngx_close_file_n " \"%V\" failed", name);
}
goto add_event;
}
ngx_rbtree_delete(&cache->rbtree, &file->node);
cache->current--;
file->close = 1;
goto create;
}
/* not found */
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc != NGX_OK && (of->err == 0 || !of->errors)) {
goto failed;
}
create:
if (cache->current >= cache->max) {
ngx_expire_old_cached_files(cache, 0, pool->log);
}
file = ngx_alloc(sizeof(ngx_cached_open_file_t), pool->log);
if (file == NULL) {
goto failed;
}
file->name = ngx_alloc(name->len + 1, pool->log);
if (file->name == NULL) {
ngx_free(file);
file = NULL;
goto failed;
}
ngx_cpystrn(file->name, name->data, name->len + 1);
file->node.key = hash;
ngx_rbtree_insert(&cache->rbtree, &file->node);
cache->current++;
file->uses = 1;
file->count = 0;
file->use_event = 0;
file->event = NULL;
add_event:
ngx_open_file_add_event(cache, file, of, pool->log);
update:
file->fd = of->fd;
file->err = of->err;
#if (NGX_HAVE_OPENAT)
file->disable_symlinks = of->disable_symlinks;
file->disable_symlinks_from = of->disable_symlinks_from;
#endif
if (of->err == 0) {
file->uniq = of->uniq;
file->mtime = of->mtime;
file->size = of->size;
file->close = 0;
file->is_dir = of->is_dir;
file->is_file = of->is_file;
file->is_link = of->is_link;
file->is_exec = of->is_exec;
file->is_directio = of->is_directio;
if (!of->is_dir) {
file->count++;
}
}
file->created = now;
found:
file->accessed = now;
ngx_queue_insert_head(&cache->expire_queue, &file->queue);
ngx_log_debug5(NGX_LOG_DEBUG_CORE, pool->log, 0,
"cached open file: %s, fd:%d, c:%d, e:%d, u:%d",
file->name, file->fd, file->count, file->err, file->uses);
if (of->err == 0) {
if (!of->is_dir) {
cln->handler = ngx_open_file_cleanup;
ofcln = cln->data;
ofcln->cache = cache;
ofcln->file = file;
ofcln->min_uses = of->min_uses;
ofcln->log = pool->log;
}
return NGX_OK;
}
return NGX_ERROR;
failed:
if (file) {
ngx_rbtree_delete(&cache->rbtree, &file->node);
cache->current--;
if (file->count == 0) {
if (file->fd != NGX_INVALID_FILE) {
if (ngx_close_file(file->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,
ngx_close_file_n " \"%s\" failed",
file->name);
}
}
ngx_free(file->name);
ngx_free(file);
} else {
file->close = 1;
}
}
if (of->fd != NGX_INVALID_FILE) {
if (ngx_close_file(of->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,
ngx_close_file_n " \"%V\" failed", name);
}
}
return NGX_ERROR;
}nginx静态文件缓存的主要代码都包含在本函数中。下面我们详细介绍一下：
1） 处理cache为NULL时的特殊情况
ngx_int_t
ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool)
{
...
if (cache == NULL) {
if (of->test_only) {
if (ngx_file_info_wrapper(name, of, &fi, pool->log)
== NGX_FILE_ERROR)
{
return NGX_ERROR;
}
of->uniq = ngx_file_uniq(&fi);
of->mtime = ngx_file_mtime(&fi);
of->size = ngx_file_size(&fi);
of->fs_size = ngx_file_fs_size(&fi);
of->is_dir = ngx_is_dir(&fi);
of->is_file = ngx_is_file(&fi);
of->is_link = ngx_is_link(&fi);
of->is_exec = ngx_is_exec(&fi);
return NGX_OK;
}
cln = ngx_pool_cleanup_add(pool, sizeof(ngx_pool_cleanup_file_t));
if (cln == NULL) {
return NGX_ERROR;
}
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc == NGX_OK && !of->is_dir) {
cln->handler = ngx_pool_cleanup_file;
clnf = cln->data;
clnf->fd = of->fd;
clnf->name = name->data;
clnf->log = pool->log;
}
return rc;
}
...
}一般只有在临时情况下传递的cache参数才会为NULL，这种情况通常只是简单获取ngx_open_file_info_t信息。此种情况下我们看到也会从pool池中申请一块小内存来管理打开文件的清除操作，但是注意这里绑定的handler也只是单个文件的关闭，与上面我们介绍的 ‘清除cache中的所有打开的缓存文件’是不同的。
2) 查找文件
ngx_int_t
ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool)
{
...
cln = ngx_pool_cleanup_add(pool, sizeof(ngx_open_file_cache_cleanup_t));
if (cln == NULL) {
return NGX_ERROR;
}
now = ngx_time();
hash = ngx_crc32_long(name->data, name->len);
file = ngx_open_file_lookup(cache, name, hash);
...
}这里首先会从池中申请一小块ngx_open_file_cache_cleanup_t空间，用于清除单个打开的文件，我们可以从后边所绑定的handler看出其中的不同。接着通过要打开的文件名name来从红黑树中查找相应的缓存。这里我们注意到，是对文件名做crc32之后，来进行查找的，也即是说红黑树中所存储信息的key是crc32(file_name)。
3) 缓存文件查找成功
ngx_int_t
ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool)
{
...
if (file) {
file->uses++;
ngx_queue_remove(&file->queue);
if (file->fd == NGX_INVALID_FILE && file->err == 0 && !file->is_dir) {
/* file was not used often enough to keep open */
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc != NGX_OK && (of->err == 0 || !of->errors)) {
goto failed;
}
goto add_event;
}
if (file->use_event
|| (file->event == NULL
&& (of->uniq == 0 || of->uniq == file->uniq)
&& now - file->created < of->valid
#if (NGX_HAVE_OPENAT)
&& of->disable_symlinks == file->disable_symlinks
&& of->disable_symlinks_from == file->disable_symlinks_from
#endif
))
{
if (file->err == 0) {
of->fd = file->fd;
of->uniq = file->uniq;
of->mtime = file->mtime;
of->size = file->size;
of->is_dir = file->is_dir;
of->is_file = file->is_file;
of->is_link = file->is_link;
of->is_exec = file->is_exec;
of->is_directio = file->is_directio;
if (!file->is_dir) {
file->count++;
ngx_open_file_add_event(cache, file, of, pool->log);
}
} else {
of->err = file->err;
#if (NGX_HAVE_OPENAT)
of->failed = file->disable_symlinks ? ngx_openat_file_n
: ngx_open_file_n;
#else
of->failed = ngx_open_file_n;
#endif
}
goto found;
}
ngx_log_debug4(NGX_LOG_DEBUG_CORE, pool->log, 0,
"retest open file: %s, fd:%d, c:%d, e:%d",
file->name, file->fd, file->count, file->err);
if (file->is_dir) {
/*
* chances that directory became file are very small
* so test_dir flag allows to use a single syscall
* in ngx_file_info() instead of three syscalls
*/
of->test_dir = 1;
}
of->fd = file->fd;
of->uniq = file->uniq;
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc != NGX_OK && (of->err == 0 || !of->errors)) {
goto failed;
}
if (of->is_dir) {
if (file->is_dir || file->err) {
goto update;
}
/* file became directory */
} else if (of->err == 0) { /* file */
if (file->is_dir || file->err) {
goto add_event;
}
if (of->uniq == file->uniq) {
if (file->event) {
file->use_event = 1;
}
of->is_directio = file->is_directio;
goto update;
}
/* file was changed */
} else { /* error to cache */
if (file->err || file->is_dir) {
goto update;
}
/* file was removed, etc. */
}
if (file->count == 0) {
ngx_open_file_del_event(file);
if (ngx_close_file(file->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,
ngx_close_file_n " \"%V\" failed", name);
}
goto add_event;
}
ngx_rbtree_delete(&cache->rbtree, &file->node);
cache->current--;
file->close = 1;
goto create;
}
...
}在第2）步中，我们会从红黑树中查找文件。如果查找成功，那么使用对应的fd来获取文件的最新信息，然后更新缓存并返回。另外：
if (file->use_event
|| (file->event == NULL
&& (of->uniq == 0 || of->uniq == file->uniq)
&& now - file->created < of->valid
#if (NGX_HAVE_OPENAT)
&& of->disable_symlinks == file->disable_symlinks
&& of->disable_symlinks_from == file->disable_symlinks_from
#endif
))
{
//处理支持文件事件的情况，即VNODE事件
goto found;
}
//不支持文件事件，则根据需要打开文件以获得相应的信息
rc = ngx_open_and_stat_file(name, of, pool->log);4） cache中文件未找到
ngx_int_t
ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool)
{
...
/* not found */
rc = ngx_open_and_stat_file(name, of, pool->log);
if (rc != NGX_OK && (of->err == 0 || !of->errors)) {
goto failed;
}
create:
if (cache->current >= cache->max) {
ngx_expire_old_cached_files(cache, 0, pool->log);
}
file = ngx_alloc(sizeof(ngx_cached_open_file_t), pool->log);
if (file == NULL) {
goto failed;
}
file->name = ngx_alloc(name->len + 1, pool->log);
if (file->name == NULL) {
ngx_free(file);
file = NULL;
goto failed;
}
ngx_cpystrn(file->name, name->data, name->len + 1);
file->node.key = hash;
ngx_rbtree_insert(&cache->rbtree, &file->node);
cache->current++;
file->uses = 1;
file->count = 0;
file->use_event = 0;
file->event = NULL;
...
}此处，cache中未找到对应的缓存文件，那么Nginx就会打开该文件，然后将其存入缓存中。这里我们注意到cache->current达到了指定的最大值时，Nginx就会强制淘汰若干个（3个以下）文件。
5) 更新相应文件信息，并插入到超时队列
ngx_int_t
ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool)
{
...
add_event:
ngx_open_file_add_event(cache, file, of, pool->log);
update:
file->fd = of->fd;
file->err = of->err;
#if (NGX_HAVE_OPENAT)
file->disable_symlinks = of->disable_symlinks;
file->disable_symlinks_from = of->disable_symlinks_from;
#endif
if (of->err == 0) {
file->uniq = of->uniq;
file->mtime = of->mtime;
file->size = of->size;
file->close = 0;
file->is_dir = of->is_dir;
file->is_file = of->is_file;
file->is_link = of->is_link;
file->is_exec = of->is_exec;
file->is_directio = of->is_directio;
if (!of->is_dir) {
file->count++;
}
}
file->created = now;
found:
file->accessed = now;
ngx_queue_insert_head(&cache->expire_queue, &file->queue);
ngx_log_debug5(NGX_LOG_DEBUG_CORE, pool->log, 0,
"cached open file: %s, fd:%d, c:%d, e:%d, u:%d",
file->name, file->fd, file->count, file->err, file->uses);
if (of->err == 0) {
if (!of->is_dir) {
cln->handler = ngx_open_file_cleanup;
ofcln = cln->data;
ofcln->cache = cache;
ofcln->file = file;
ofcln->min_uses = of->min_uses;
ofcln->log = pool->log;
}
return NGX_OK;
}
return NGX_ERROR;
...
}此处，更新前面获取到的文件信息到file变量，然后再插入到超时队列。值得注意的是，这里同样会为该打开的缓存文件绑定一个缓存清除回调函数。
6） 处理失败情况
ngx_int_t
ngx_open_cached_file(ngx_open_file_cache_t *cache, ngx_str_t *name,
ngx_open_file_info_t *of, ngx_pool_t *pool)
{
...
failed:
if (file) {
ngx_rbtree_delete(&cache->rbtree, &file->node);
cache->current--;
if (file->count == 0) {
if (file->fd != NGX_INVALID_FILE) {
if (ngx_close_file(file->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,
ngx_close_file_n " \"%s\" failed",
file->name);
}
}
ngx_free(file->name);
ngx_free(file);
} else {
file->close = 1;
}
}
if (of->fd != NGX_INVALID_FILE) {
if (ngx_close_file(of->fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, pool->log, ngx_errno,
ngx_close_file_n " \"%V\" failed", name);
}
}
return NGX_ERROR;
...
}处理失败时，从缓存中清除相应的缓存信息，并关闭对应的文件句柄。
7. 函数
#if (NGX_HAVE_OPENAT)
static ngx_fd_t
ngx_openat_file_owner(ngx_fd_t at_fd, const u_char *name,
ngx_int_t mode, ngx_int_t create, ngx_int_t access, ngx_log_t *log)
{
ngx_fd_t fd;
ngx_err_t err;
ngx_file_info_t fi, atfi;
/*
* To allow symlinks with the same owner, use openat() (followed
* by fstat()) and fstatat(AT_SYMLINK_NOFOLLOW), and then compare
* uids between fstat() and fstatat().
*
* As there is a race between openat() and fstatat() we don't
* know if openat() in fact opened symlink or not. Therefore,
* we have to compare uids even if fstatat() reports the opened
* component isn't a symlink (as we don't know whether it was
* symlink during openat() or not).
*/
fd = ngx_openat_file(at_fd, name, mode, create, access);
if (fd == NGX_INVALID_FILE) {
return NGX_INVALID_FILE;
}
if (ngx_file_at_info(at_fd, name, &atfi, AT_SYMLINK_NOFOLLOW)
== NGX_FILE_ERROR)
{
err = ngx_errno;
goto failed;
}
#if (NGX_HAVE_O_PATH)
if (ngx_file_o_path_info(fd, &fi, log) == NGX_ERROR) {
err = ngx_errno;
goto failed;
}
#else
if (ngx_fd_info(fd, &fi) == NGX_FILE_ERROR) {
err = ngx_errno;
goto failed;
}
#endif
if (fi.st_uid != atfi.st_uid) {
err = NGX_ELOOP;
goto failed;
}
return fd;
failed:
if (ngx_close_file(fd) == NGX_FILE_ERROR) {
ngx_log_error(NGX_LOG_ALERT, log, ngx_errno,
ngx_close_file_n " \"%s\" failed", name);
}
ngx_set_errno(err);
return NGX_INVALID_FILE;
}
#endif这里由于openat()并不能判断出所打开的文件是否是一个链接文件，因此必须要比较fstat()与fstatat()获取到的owner信息。
8. 函数ngx_file_o_path_info()
#if (NGX_HAVE_OPENAT)
#if (NGX_HAVE_O_PATH)
static ngx_int_t
ngx_file_o_path_info(ngx_fd_t fd, ngx_file_info_t *fi, ngx_log_t *log)
{
static ngx_uint_t use_fstat = 1;
/*
* In Linux 2.6.39 the O_PATH flag was introduced that allows to obtain
* a descriptor without actually opening file or directory. It requires
* less permissions for path components, but till Linux 3.6 fstat() returns
* EBADF on such descriptors, and fstatat() with the AT_EMPTY_PATH flag
* should be used instead.
*
* Three scenarios are handled in this function:
*
* 1) The kernel is newer than 3.6 or fstat() with O_PATH support was
* backported by vendor. Then fstat() is used.
*
* 2) The kernel is newer than 2.6.39 but older than 3.6. In this case
* the first call of fstat() returns EBADF and we fallback to fstatat()
* with AT_EMPTY_PATH which was introduced at the same time as O_PATH.
*
* 3) The kernel is older than 2.6.39 but nginx was build with O_PATH
* support. Since descriptors are opened with O_PATH|O_RDONLY flags
* and O_PATH is ignored by the kernel then the O_RDONLY flag is
* actually used. In this case fstat() just works.
*/
if (use_fstat) {
if (ngx_fd_info(fd, fi) != NGX_FILE_ERROR) {
return NGX_OK;
}
if (ngx_errno != NGX_EBADF) {
return NGX_ERROR;
}
ngx_log_error(NGX_LOG_NOTICE, log, 0,
"fstat(O_PATH) failed with EBADF, "
"switching to fstatat(AT_EMPTY_PATH)");
use_fstat = 0;
}
if (ngx_file_at_info(fd, "", fi, AT_EMPTY_PATH) != NGX_FILE_ERROR) {
return NGX_OK;
}
return NGX_ERROR;
}
#endif
#endif /* NGX_HAVE_OPENAT */此函数也主要用于支持使用openat()函数来获取文件信息。
[参看]
