nginx 文件读取和写入方式

打开：

 fd = ngx_open_file(filename->data, NGX_FILE_RDONLY, NGX_FILE_OPEN, 0);

#define ngx_open_file(name, mode, create, access)                            \
    open((const char *) name, mode|create, access)

获取文件的信息：

 if (ngx_fd_info(fd, &cf->conf_file->file.info) == -1) {

#define ngx_fd_info(fd, sb)      fstat(fd, sb)

读取：

 //从文件里面读取信息
n = ngx_read_file(&cf->conf_file->file, b->start + len, size,  cf->conf_file->file.offset);

ssize_t
ngx_read_file(ngx_file_t *file, u_char *buf, size_t size, off_t offset)
{
    ssize_t  n;

    ngx_log_debug4(NGX_LOG_DEBUG_CORE, file->log, 0,
                   "read: %d, %p, %uz, %O", file->fd, buf, size, offset);

#if (NGX_HAVE_PREAD)

    n = pread(file->fd, buf, size, offset); //从偏移量开始读数据，第一次把所有的东西都读出来

    if (n == -1) {
        ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno,
                      "pread() \"%s\" failed", file->name.data);
        return NGX_ERROR;
    }

#else

    if (file->sys_offset != offset) {
        if (lseek(file->fd, offset, SEEK_SET) == -1) {
            ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno,
                          "lseek() \"%s\" failed", file->name.data);
            return NGX_ERROR;
        }

        file->sys_offset = offset;
    }

    n = read(file->fd, buf, size);

    if (n == -1) {
        ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno,
                      "read() \"%s\" failed", file->name.data);
        return NGX_ERROR;
    }

    file->sys_offset += n;

#endif

    file->offset += n;

    return n;
}

写入文件：

ssize_t
ngx_write_file(ngx_file_t *file, u_char *buf, size_t size, off_t offset)
{
    ssize_t  n, written;

    ngx_log_debug4(NGX_LOG_DEBUG_CORE, file->log, 0,
                   "write: %d, %p, %uz, %O", file->fd, buf, size, offset);

    written = 0;

#if (NGX_HAVE_PWRITE)

    for ( ;; ) {
        n = pwrite(file->fd, buf + written, size, offset);

        if (n == -1) {
            ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno,
                          "pwrite() \"%s\" failed", file->name.data);
            return NGX_ERROR;
        }

        file->offset += n;
        written += n;

        if ((size_t) n == size) {
            return written;
        }

        offset += n;
        size -= n;
    }

#else

    if (file->sys_offset != offset) {
        if (lseek(file->fd, offset, SEEK_SET) == -1) {
            ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno,
                          "lseek() \"%s\" failed", file->name.data);
            return NGX_ERROR;
        }

        file->sys_offset = offset;
    }

    for ( ;; ) {
        n = write(file->fd, buf + written, size);

        if (n == -1) {
            ngx_log_error(NGX_LOG_CRIT, file->log, ngx_errno,
                          "write() \"%s\" failed", file->name.data);
            return NGX_ERROR;
        }

        file->offset += n;
        written += n;

        if ((size_t) n == size) {
            return written;
        }

        size -= n;
    }
#endif
}