On 2022/11/19 2:06, Kang-Che Sung wrote:
On Friday, November 18, 2022, Xiaoming Ni <[email protected]
<mailto:[email protected]>> wrote:
> Step 6 of micro-refactoring the set_loop():
> Use structs to avoid transferring a large number of parameters
> in set_loop_configure() and set_loop_info()
>
> function old new delta
> set_loop 708 720 +12
>
------------------------------------------------------------------------------
> (add/remove: 0/0 grow/shrink: 1/0 up/down: 12/0) Total:
12 bytes
>
> Signed-off-by: Xiaoming Ni <[email protected]
<mailto:[email protected]>>
> ---
> libbb/loop.c | 54 +++++++++++++++++++++++++++++-----------------------
> 1 file changed, 30 insertions(+), 24 deletions(-)
>
...
> - */
> - loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY);
> - rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
> - if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {
> + rc = ioctl(lfd, BB_LOOP_SET_STATUS, loopinfo);
> + if (rc != 0 && (loopinfo->lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {
> + memcpy(&loopinfo2, loopinfo, sizeof(*loopinfo));
Just use `loopinfo2 = loopinfo;`
Tested on my PC, there was no difference in code size between your
modified scheme and my current scheme.
function old new delta
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0) Total: 0
bytes
Also, it is unclear why there is the need to clone the loopinfo buffer.
> /* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */
> /* (this code path is not tested) */
> - loopinfo.lo_flags -= BB_LO_FLAGS_AUTOCLEAR;
> - rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo);
> + loopinfo2.lo_flags -= BB_LO_FLAGS_AUTOCLEAR;
> + rc = ioctl(lfd, BB_LOOP_SET_STATUS, &loopinfo2);
> }
> if (rc == 0) {
> return lfd;
...
>
> +static void init_bb_loop_info(bb_loop_info *loopinfo, const char *file,
> + unsigned long long offset, unsigned long long
sizelimit, unsigned flags)
> +{
> + memset(loopinfo, 0, sizeof(*loopinfo));
Would it reduce code size by doing the initialization like this?
```
bb_loop_info empty = {0};
loopinfo = empty;
```
Tested on my PC, there was no difference in code size between your
modified scheme and my current scheme.
function old new delta
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0) Total: 0
bytes
Thanks
Xiaoming Ni
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