Hello!

On Tue, Jul 24, 2012 at 03:34:39PM +0800, 姚伟斌 wrote:

> 1. The type of 'ngx_msec_int_t', from the source code, It's defined like this:
>
> typedef ngx_int_t ngx_rbtree_key_int_t;
> typedef ngx_rbtree_key_int_t ngx_msec_int_t;
>
> So It should be an ngx_int_t.
>
> In the file of ngx_http_log_module.c, It appears like this:
>
> static u_char *
> ngx_http_log_request_time(ngx_http_request_t *r, u_char *buf,
> ngx_http_log_op_t *op)
> {
> ngx_time_t *tp;
> ngx_msec_int_t ms;
>
> tp = ngx_timeofday();
>
> ms = (ngx_msec_int_t)
> ((tp->sec - r->start_sec) * 1000 + (tp->msec - r->start_msec));
> ms = ngx_max(ms, 0);
>
> return ngx_sprintf(buf, "%T.%03M", ms / 1000, ms % 1000);
> }

In case of ngx_msec_int_t it's almost always possible to use %M
which has identical size, as it's only used for intermediate
computations and ensured to be non-negative. (Note the
ngx_max(ms, 0) call in the code above.)

> 2. The type of '' ngx_gid_t" and "ngx_uid_t", from the source code.
> They are defined like this:
>
> typedef uid_t ngx_uid_t;
> typedef gid_t ngx_gid_t;
>
> And I googled [1][2] about the types of uid_t and gid_t and They seem
> to unsigned integer.

Just a side note: no, POSIX doesn't define signedness of
uid_t/gid_t. It only says they should be "integer types", see
http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_types.h.html.

>
> In the file of ngx_process_cycle.c, it appears like this:
>
> if (geteuid() == 0) {
> if (setgid(ccf->group) == -1) {
> ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
> "setgid(%d) failed", ccf->group);
> /* fatal */
> exit(2);
> }
>
> if (initgroups(ccf->username, ccf->group) == -1) {
> ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
> "initgroups(%s, %d) failed",
> ccf->username, ccf->group);
> }
>
> if (setuid(ccf->user) == -1) {
> ngx_log_error(NGX_LOG_EMERG, cycle->log, ngx_errno,
> "setuid(%d) failed", ccf->user);
> /* fatal */
> exit(2);
> }
> }
>
> I want to know the correct format specifiers with ngx_msec_int_t,
> uid_t and gid_t. I'm a little confused with above codes.

See above for ngx_msec_int_t. Most safe way to print
ngx_uint_t/ngx_gid_t is probably to do so with intermediate cast
to some defined big-enough type.

Strictly speaking the above code isn't correct and might print
garbage on some platforms. It probably worth adding explicit
casts to int.

Maxim Dounin

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