linux-kernel - Re: [PATCH 2/2] gfs2: replace usage of found with dedicated list iterator variable

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Date:   Mon, 4 Apr 2022 16:42:03 +0200
From:   Andreas Gruenbacher <agruenba@...hat.com>
To:     Jakob Koschel <jakobkoschel@...il.com>
Cc:     Bob Peterson <rpeterso@...hat.com>,
        cluster-devel <cluster-devel@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH 2/2] gfs2: replace usage of found with dedicated list
 iterator variable

Jakob,

On Fri, Apr 1, 2022 at 12:40 AM Jakob Koschel <jakobkoschel@...il.com> wrote:
> To move the list iterator variable into the list_for_each_entry_*()
> macro in the future it should be avoided to use the list iterator
> variable after the loop body.
>
> To *never* use the list iterator variable after the loop it was
> concluded to use a separate iterator variable instead of a
> found boolean [1].
>
> This removes the need to use a found variable and simply checking if
> the variable was set, can determine if the break/goto was hit.
>
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
> Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
> ---
>  fs/gfs2/quota.c    | 13 ++++++-------
>  fs/gfs2/recovery.c | 22 ++++++++++------------
>  2 files changed, 16 insertions(+), 19 deletions(-)
>
> diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
> index be0997e24d60..dafd04fb9164 100644
> --- a/fs/gfs2/quota.c
> +++ b/fs/gfs2/quota.c
> @@ -443,7 +443,7 @@ static int qd_check_sync(struct gfs2_sbd *sdp, struct gfs2_quota_data *qd,
>
>  static int qd_fish(struct gfs2_sbd *sdp, struct gfs2_quota_data **qdp)
>  {
> -       struct gfs2_quota_data *qd = NULL;
> +       struct gfs2_quota_data *qd = NULL, *iter;
>         int error;
>         int found = 0;
>
> @@ -454,15 +454,14 @@ static int qd_fish(struct gfs2_sbd *sdp, struct gfs2_quota_data **qdp)
>
>         spin_lock(&qd_lock);
>
> -       list_for_each_entry(qd, &sdp->sd_quota_list, qd_list) {
> -               found = qd_check_sync(sdp, qd, &sdp->sd_quota_sync_gen);
> -               if (found)
> +       list_for_each_entry(iter, &sdp->sd_quota_list, qd_list) {
> +               found = qd_check_sync(sdp, iter, &sdp->sd_quota_sync_gen);
> +               if (found) {
> +                       qd = iter;

we might as well get rid of 'found' here like in the below two
changes. Let me fix that up.

>                         break;
> +               }
>         }
>
> -       if (!found)
> -               qd = NULL;
> -
>         spin_unlock(&qd_lock);
>
>         if (qd) {
> diff --git a/fs/gfs2/recovery.c b/fs/gfs2/recovery.c
> index 016ed1b2ca1d..2bb085a72e8e 100644
> --- a/fs/gfs2/recovery.c
> +++ b/fs/gfs2/recovery.c
> @@ -55,17 +55,16 @@ int gfs2_replay_read_block(struct gfs2_jdesc *jd, unsigned int blk,
>  int gfs2_revoke_add(struct gfs2_jdesc *jd, u64 blkno, unsigned int where)
>  {
>         struct list_head *head = &jd->jd_revoke_list;
> -       struct gfs2_revoke_replay *rr;
> -       int found = 0;
> +       struct gfs2_revoke_replay *rr = NULL, *iter;
>
> -       list_for_each_entry(rr, head, rr_list) {
> -               if (rr->rr_blkno == blkno) {
> -                       found = 1;
> +       list_for_each_entry(iter, head, rr_list) {
> +               if (iter->rr_blkno == blkno) {
> +                       rr = iter;
>                         break;
>                 }
>         }
>
> -       if (found) {
> +       if (rr) {
>                 rr->rr_where = where;
>                 return 0;
>         }
> @@ -83,18 +82,17 @@ int gfs2_revoke_add(struct gfs2_jdesc *jd, u64 blkno, unsigned int where)
>
>  int gfs2_revoke_check(struct gfs2_jdesc *jd, u64 blkno, unsigned int where)
>  {
> -       struct gfs2_revoke_replay *rr;
> +       struct gfs2_revoke_replay *rr = NULL, *iter;
>         int wrap, a, b, revoke;
> -       int found = 0;
>
> -       list_for_each_entry(rr, &jd->jd_revoke_list, rr_list) {
> -               if (rr->rr_blkno == blkno) {
> -                       found = 1;
> +       list_for_each_entry(iter, &jd->jd_revoke_list, rr_list) {
> +               if (iter->rr_blkno == blkno) {
> +                       rr = iter;
>                         break;
>                 }
>         }
>
> -       if (!found)
> +       if (!rr)
>                 return 0;
>
>         wrap = (rr->rr_where < jd->jd_replay_tail);
> --
> 2.25.1
>

Thanks,
Andreas