[PATCH v3 0/2] md: simplify md_seq_ops

[PATCH v3 0/2] md: simplify md_seq_ops

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Changes in v3:
 - rework patch 1, because the condition is confusing

Changes in v2:
 - don't hold lock while show mddev in md_seq_show
 - add patch 1
 - add commit message

Yu Kuai (2):
  md: factor out a helper from mddev_put()
  md: simplify md_seq_ops

 drivers/md/md.c | 129 +++++++++++++++---------------------------------
 1 file changed, 39 insertions(+), 90 deletions(-)

-- 
2.39.2

[PATCH v3 1/2] md: factor out a helper from mddev_put()

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

There are no functional changes, prepare to simplify md_seq_ops in next
patch.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 10cb4dfbf4ae..73782cafad4e 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -616,23 +616,28 @@ static inline struct mddev *mddev_get(struct mddev *mddev)
 
 static void mddev_delayed_delete(struct work_struct *ws);
 
+static void __mddev_put(struct mddev *mddev)
+{
+	if (mddev->raid_disks || !list_empty(&mddev->disks) ||
+	    mddev->ctime || mddev->hold_active)
+		return;
+
+	/* Array is not configured at all, and not held active, so destroy it */
+	set_bit(MD_DELETED, &mddev->flags);
+
+	/*
+	 * Call queue_work inside the spinlock so that flush_workqueue() after
+	 * mddev_find will succeed in waiting for the work to be done.
+	 */
+	queue_work(md_misc_wq, &mddev->del_work);
+}
+
 void mddev_put(struct mddev *mddev)
 {
 	if (!atomic_dec_and_lock(&mddev->active, &all_mddevs_lock))
 		return;
-	if (!mddev->raid_disks && list_empty(&mddev->disks) &&
-	    mddev->ctime == 0 && !mddev->hold_active) {
-		/* Array is not configured at all, and not held active,
-		 * so destroy it */
-		set_bit(MD_DELETED, &mddev->flags);
 
-		/*
-		 * Call queue_work inside the spinlock so that
-		 * flush_workqueue() after mddev_find will succeed in waiting
-		 * for the work to be done.
-		 */
-		queue_work(md_misc_wq, &mddev->del_work);
-	}
+	__mddev_put(mddev);
 	spin_unlock(&all_mddevs_lock);
 }
 
-- 
2.39.2

[PATCH v3 2/2] md: simplify md_seq_ops

[Yu Kuai]

From: Yu Kuai <yukuai3@huawei.com>

Before this patch, the implementation is hacky and hard to understand:

1) md_seq_start set pos to 1;
2) md_seq_show found pos is 1, then print Personalities;
3) md_seq_next found pos is 1, then it update pos to the first mddev;
4) md_seq_show found pos is not 1 or 2, show mddev;
5) md_seq_next found pos is not 1 or 2, update pos to next mddev;
6) loop 4-5 until the last mddev, then md_seq_next update pos to 2;
7) md_seq_show found pos is 2, then print unused devices;
8) md_seq_next found pos is 2, stop;

This patch remove the magic value and use seq_list_start/next/stop()
directly, and move printing "Personalities" to md_seq_start(),
"unsed devices" to md_seq_stop():

1) md_seq_start print Personalities, and then set pos to first mddev;
2) md_seq_show show mddev;
3) md_seq_next update pos to next mddev;
4) loop 2-3 until the last mddev;
5) md_seq_stop print unsed devices;

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/md/md.c | 100 +++++++++++-------------------------------------
 1 file changed, 22 insertions(+), 78 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 73782cafad4e..0b83a406e797 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8213,105 +8213,46 @@ static int status_resync(struct seq_file *seq, struct mddev *mddev)
 }
 
 static void *md_seq_start(struct seq_file *seq, loff_t *pos)
+	__acquires(&all_mddevs_lock)
 {
-	struct list_head *tmp;
-	loff_t l = *pos;
-	struct mddev *mddev;
+	struct md_personality *pers;
 
-	if (l == 0x10000) {
-		++*pos;
-		return (void *)2;
-	}
-	if (l > 0x10000)
-		return NULL;
-	if (!l--)
-		/* header */
-		return (void*)1;
+	seq_puts(seq, "Personalities : ");
+	spin_lock(&pers_lock);
+	list_for_each_entry(pers, &pers_list, list)
+		seq_printf(seq, "[%s] ", pers->name);
+
+	spin_unlock(&pers_lock);
+	seq_puts(seq, "\n");
+	seq->poll_event = atomic_read(&md_event_count);
 
 	spin_lock(&all_mddevs_lock);
-	list_for_each(tmp,&all_mddevs)
-		if (!l--) {
-			mddev = list_entry(tmp, struct mddev, all_mddevs);
-			if (!mddev_get(mddev))
-				continue;
-			spin_unlock(&all_mddevs_lock);
-			return mddev;
-		}
-	spin_unlock(&all_mddevs_lock);
-	if (!l--)
-		return (void*)2;/* tail */
-	return NULL;
+
+	return seq_list_start(&all_mddevs, *pos);
 }
 
 static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 {
-	struct list_head *tmp;
-	struct mddev *next_mddev, *mddev = v;
-	struct mddev *to_put = NULL;
-
-	++*pos;
-	if (v == (void*)2)
-		return NULL;
-
-	spin_lock(&all_mddevs_lock);
-	if (v == (void*)1) {
-		tmp = all_mddevs.next;
-	} else {
-		to_put = mddev;
-		tmp = mddev->all_mddevs.next;
-	}
-
-	for (;;) {
-		if (tmp == &all_mddevs) {
-			next_mddev = (void*)2;
-			*pos = 0x10000;
-			break;
-		}
-		next_mddev = list_entry(tmp, struct mddev, all_mddevs);
-		if (mddev_get(next_mddev))
-			break;
-		mddev = next_mddev;
-		tmp = mddev->all_mddevs.next;
-	}
-	spin_unlock(&all_mddevs_lock);
-
-	if (to_put)
-		mddev_put(to_put);
-	return next_mddev;
-
+	return seq_list_next(v, &all_mddevs, pos);
 }
 
 static void md_seq_stop(struct seq_file *seq, void *v)
+	__releases(&all_mddevs_lock)
 {
-	struct mddev *mddev = v;
-
-	if (mddev && v != (void*)1 && v != (void*)2)
-		mddev_put(mddev);
+	status_unused(seq);
+	spin_unlock(&all_mddevs_lock);
 }
 
 static int md_seq_show(struct seq_file *seq, void *v)
 {
-	struct mddev *mddev = v;
+	struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
 	sector_t sectors;
 	struct md_rdev *rdev;
 
-	if (v == (void*)1) {
-		struct md_personality *pers;
-		seq_printf(seq, "Personalities : ");
-		spin_lock(&pers_lock);
-		list_for_each_entry(pers, &pers_list, list)
-			seq_printf(seq, "[%s] ", pers->name);
-
-		spin_unlock(&pers_lock);
-		seq_printf(seq, "\n");
-		seq->poll_event = atomic_read(&md_event_count);
+	if (!mddev_get(mddev))
 		return 0;
-	}
-	if (v == (void*)2) {
-		status_unused(seq);
-		return 0;
-	}
 
+	spin_unlock(&all_mddevs_lock);
 	spin_lock(&mddev->lock);
 	if (mddev->pers || mddev->raid_disks || !list_empty(&mddev->disks)) {
 		seq_printf(seq, "%s : %sactive", mdname(mddev),
@@ -8382,6 +8323,9 @@ static int md_seq_show(struct seq_file *seq, void *v)
 		seq_printf(seq, "\n");
 	}
 	spin_unlock(&mddev->lock);
+	spin_lock(&all_mddevs_lock);
+	if (atomic_dec_and_test(&mddev->active))
+		__mddev_put(mddev);
 
 	return 0;
 }
-- 
2.39.2

Re: [PATCH v3 0/2] md: simplify md_seq_ops

[Song Liu]

On Tue, Sep 26, 2023 at 11:19 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> Changes in v3:
>  - rework patch 1, because the condition is confusing
>
> Changes in v2:
>  - don't hold lock while show mddev in md_seq_show
>  - add patch 1
>  - add commit message

Applied to md-next. Thanks!

Song

>
> Yu Kuai (2):
>   md: factor out a helper from mddev_put()
>   md: simplify md_seq_ops
>
>  drivers/md/md.c | 129 +++++++++++++++---------------------------------
>  1 file changed, 39 insertions(+), 90 deletions(-)
>
> --
> 2.39.2
>

Re: [PATCH v3 2/2] md: simplify md_seq_ops

[Song Liu]

On Tue, Sep 26, 2023 at 11:19 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> From: Yu Kuai <yukuai3@huawei.com>
>
> Before this patch, the implementation is hacky and hard to understand:
>
> 1) md_seq_start set pos to 1;
> 2) md_seq_show found pos is 1, then print Personalities;
> 3) md_seq_next found pos is 1, then it update pos to the first mddev;
> 4) md_seq_show found pos is not 1 or 2, show mddev;
> 5) md_seq_next found pos is not 1 or 2, update pos to next mddev;
> 6) loop 4-5 until the last mddev, then md_seq_next update pos to 2;
> 7) md_seq_show found pos is 2, then print unused devices;
> 8) md_seq_next found pos is 2, stop;
>
> This patch remove the magic value and use seq_list_start/next/stop()
> directly, and move printing "Personalities" to md_seq_start(),
> "unsed devices" to md_seq_stop():
>
> 1) md_seq_start print Personalities, and then set pos to first mddev;
> 2) md_seq_show show mddev;
> 3) md_seq_next update pos to next mddev;
> 4) loop 2-3 until the last mddev;
> 5) md_seq_stop print unsed devices;
>
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>

Just realized this introduced a behavior change:

When there is not md devices, before this patch, we have

[root@eth50-1 ~]# cat /proc/mdstat
Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
unused devices: <none>

After this patch, "cat /proc/mdstat" returns nothing. This causes
some confusion for users who want to read "Personalities" line,
for example, the mdadm test suite reads it.

I haven't figured out the best fix yet.

Thanks,
Song

Re: [PATCH v3 2/2] md: simplify md_seq_ops

[Yu Kuai]

Hi,

在 2024/01/09 7:38, Song Liu 写道:
> On Tue, Sep 26, 2023 at 11:19 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> Before this patch, the implementation is hacky and hard to understand:
>>
>> 1) md_seq_start set pos to 1;
>> 2) md_seq_show found pos is 1, then print Personalities;
>> 3) md_seq_next found pos is 1, then it update pos to the first mddev;
>> 4) md_seq_show found pos is not 1 or 2, show mddev;
>> 5) md_seq_next found pos is not 1 or 2, update pos to next mddev;
>> 6) loop 4-5 until the last mddev, then md_seq_next update pos to 2;
>> 7) md_seq_show found pos is 2, then print unused devices;
>> 8) md_seq_next found pos is 2, stop;
>>
>> This patch remove the magic value and use seq_list_start/next/stop()
>> directly, and move printing "Personalities" to md_seq_start(),
>> "unsed devices" to md_seq_stop():
>>
>> 1) md_seq_start print Personalities, and then set pos to first mddev;
>> 2) md_seq_show show mddev;
>> 3) md_seq_next update pos to next mddev;
>> 4) loop 2-3 until the last mddev;
>> 5) md_seq_stop print unsed devices;
>>
>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> 
> Just realized this introduced a behavior change:
> 
> When there is not md devices, before this patch, we have
> 
> [root@eth50-1 ~]# cat /proc/mdstat
> Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
> unused devices: <none>
> 
> After this patch, "cat /proc/mdstat" returns nothing. This causes
> some confusion for users who want to read "Personalities" line,
> for example, the mdadm test suite reads it.
> 
> I haven't figured out the best fix yet.

Yes, that's a problem. And after reviewing seq_read_iter() in detail, I
realize that I also can't use seq_printf() in m->op->start() directly,
because if seq buffer overflowed, md_seq_start() can be called more than
once.

I'll fix these problems soon.

Thanks,
Kuai

> 
> Thanks,
> Song
> 
> .
> 

Re: [PATCH v3 2/2] md: simplify md_seq_ops

[Yu Kuai]

Hi,

在 2024/01/09 9:21, Yu Kuai 写道:
> Hi,
> 
> 在 2024/01/09 7:38, Song Liu 写道:
>> On Tue, Sep 26, 2023 at 11:19 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>>
>>> From: Yu Kuai <yukuai3@huawei.com>
>>>
>>> Before this patch, the implementation is hacky and hard to understand:
>>>
>>> 1) md_seq_start set pos to 1;
>>> 2) md_seq_show found pos is 1, then print Personalities;
>>> 3) md_seq_next found pos is 1, then it update pos to the first mddev;
>>> 4) md_seq_show found pos is not 1 or 2, show mddev;
>>> 5) md_seq_next found pos is not 1 or 2, update pos to next mddev;
>>> 6) loop 4-5 until the last mddev, then md_seq_next update pos to 2;
>>> 7) md_seq_show found pos is 2, then print unused devices;
>>> 8) md_seq_next found pos is 2, stop;
>>>
>>> This patch remove the magic value and use seq_list_start/next/stop()
>>> directly, and move printing "Personalities" to md_seq_start(),
>>> "unsed devices" to md_seq_stop():
>>>
>>> 1) md_seq_start print Personalities, and then set pos to first mddev;
>>> 2) md_seq_show show mddev;
>>> 3) md_seq_next update pos to next mddev;
>>> 4) loop 2-3 until the last mddev;
>>> 5) md_seq_stop print unsed devices;
>>>
>>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>>
>> Just realized this introduced a behavior change:
>>
>> When there is not md devices, before this patch, we have
>>
>> [root@eth50-1 ~]# cat /proc/mdstat
>> Personalities : [raid0] [raid1] [raid10] [raid6] [raid5] [raid4]
>> unused devices: <none>
>>
>> After this patch, "cat /proc/mdstat" returns nothing. This causes
>> some confusion for users who want to read "Personalities" line,
>> for example, the mdadm test suite reads it.
>>
>> I haven't figured out the best fix yet.
> 
> Yes, that's a problem. And after reviewing seq_read_iter() in detail, I
> realize that I also can't use seq_printf() in m->op->start() directly,
> because if seq buffer overflowed, md_seq_start() can be called more than
> once.
> 
> I'll fix these problems soon.
How about following patch(already tested)?

Thanks,
Kuai

diff --git a/drivers/md/md.c b/drivers/md/md.c
index e351e6c51cc7..289d3d89e73d 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -8135,6 +8135,19 @@ static void status_unused(struct seq_file *seq)
         seq_printf(seq, "\n");
  }

+static void status_personalities(struct seq_file *seq)
+{
+       struct md_personality *pers;
+
+       seq_puts(seq, "Personalities : ");
+       spin_lock(&pers_lock);
+       list_for_each_entry(pers, &pers_list, list)
+               seq_printf(seq, "[%s] ", pers->name);
+
+       spin_unlock(&pers_lock);
+       seq_puts(seq, "\n");
+}
+
  static int status_resync(struct seq_file *seq, struct mddev *mddev)
  {
         sector_t max_sectors, resync, res;
@@ -8273,43 +8286,53 @@ static int status_resync(struct seq_file *seq, 
struct mddev *mddev)
         return 1;
  }

+#define MDDEV_NONE (void *)1
+
  static void *md_seq_start(struct seq_file *seq, loff_t *pos)
         __acquires(&all_mddevs_lock)
  {
-       struct md_personality *pers;
-
-       seq_puts(seq, "Personalities : ");
-       spin_lock(&pers_lock);
-       list_for_each_entry(pers, &pers_list, list)
-               seq_printf(seq, "[%s] ", pers->name);
-
-       spin_unlock(&pers_lock);
-       seq_puts(seq, "\n");
         seq->poll_event = atomic_read(&md_event_count);
-
         spin_lock(&all_mddevs_lock);

-       return seq_list_start(&all_mddevs, *pos);
+       if (!list_empty(&all_mddevs))
+               return seq_list_start(&all_mddevs, *pos);
+       else if (*pos == 0)
+               return MDDEV_NONE;
+       else
+               return NULL;
  }

  static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
  {
+       if (v == MDDEV_NONE) {
+               ++*pos;
+               return NULL;
+       }
+
         return seq_list_next(v, &all_mddevs, pos);
  }

  static void md_seq_stop(struct seq_file *seq, void *v)
         __releases(&all_mddevs_lock)
  {
-       status_unused(seq);
         spin_unlock(&all_mddevs_lock);
  }
  static int md_seq_show(struct seq_file *seq, void *v)
  {
-       struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
+       struct mddev *mddev;
         sector_t sectors;
         struct md_rdev *rdev;

+       if (v == MDDEV_NONE) {
+               status_personalities(seq);
+               status_unused(seq);
+               return 0;
+       }
+
+       mddev = list_entry(v, struct mddev, all_mddevs);
+       if (mddev == list_first_entry(&all_mddevs, struct mddev, 
all_mddevs))
+               status_personalities(seq);
         if (!mddev_get(mddev))
                 return 0;

@@ -8385,6 +8408,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
         }
         spin_unlock(&mddev->lock);
         spin_lock(&all_mddevs_lock);
+
+       if (mddev == list_last_entry(&all_mddevs, struct mddev, all_mddevs))
+               status_unused(seq);
+
         if (atomic_dec_and_test(&mddev->active))
                 __mddev_put(mddev);




> 
> Thanks,
> Kuai
> 
>>
>> Thanks,
>> Song
>>
>> .
>>
> 
> .
> 

Re: [PATCH v3 2/2] md: simplify md_seq_ops

[Song Liu]

On Mon, Jan 8, 2024 at 11:48 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> Hi,
>
> 在 2024/01/09 9:21, Yu Kuai 写道:
> > Hi,
> >
> > 在 2024/01/09 7:38, Song Liu 写道:
> >> On Tue, Sep 26, 2023 at 11:19 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
[...]
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index e351e6c51cc7..289d3d89e73d 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -8135,6 +8135,19 @@ static void status_unused(struct seq_file *seq)
>          seq_printf(seq, "\n");
>   }
>
> +static void status_personalities(struct seq_file *seq)
> +{
> +       struct md_personality *pers;
> +
> +       seq_puts(seq, "Personalities : ");
> +       spin_lock(&pers_lock);
> +       list_for_each_entry(pers, &pers_list, list)
> +               seq_printf(seq, "[%s] ", pers->name);
> +
> +       spin_unlock(&pers_lock);
> +       seq_puts(seq, "\n");
> +}
> +
>   static int status_resync(struct seq_file *seq, struct mddev *mddev)
>   {
>          sector_t max_sectors, resync, res;
> @@ -8273,43 +8286,53 @@ static int status_resync(struct seq_file *seq,
> struct mddev *mddev)
>          return 1;
>   }
>
> +#define MDDEV_NONE (void *)1
> +
>   static void *md_seq_start(struct seq_file *seq, loff_t *pos)
>          __acquires(&all_mddevs_lock)
>   {
> -       struct md_personality *pers;
> -
> -       seq_puts(seq, "Personalities : ");
> -       spin_lock(&pers_lock);
> -       list_for_each_entry(pers, &pers_list, list)
> -               seq_printf(seq, "[%s] ", pers->name);
> -
> -       spin_unlock(&pers_lock);
> -       seq_puts(seq, "\n");
>          seq->poll_event = atomic_read(&md_event_count);
> -
>          spin_lock(&all_mddevs_lock);
>
> -       return seq_list_start(&all_mddevs, *pos);
> +       if (!list_empty(&all_mddevs))
> +               return seq_list_start(&all_mddevs, *pos);
> +       else if (*pos == 0)
> +               return MDDEV_NONE;
> +       else
> +               return NULL;
>   }
>
>   static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
>   {
> +       if (v == MDDEV_NONE) {
> +               ++*pos;
> +               return NULL;
> +       }
> +
>          return seq_list_next(v, &all_mddevs, pos);
>   }
>
>   static void md_seq_stop(struct seq_file *seq, void *v)
>          __releases(&all_mddevs_lock)
>   {
> -       status_unused(seq);
>          spin_unlock(&all_mddevs_lock);
>   }
>   static int md_seq_show(struct seq_file *seq, void *v)
>   {
> -       struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
> +       struct mddev *mddev;
>          sector_t sectors;
>          struct md_rdev *rdev;
>
> +       if (v == MDDEV_NONE) {
> +               status_personalities(seq);
> +               status_unused(seq);
> +               return 0;
> +       }
> +
> +       mddev = list_entry(v, struct mddev, all_mddevs);
> +       if (mddev == list_first_entry(&all_mddevs, struct mddev,
> all_mddevs))
> +               status_personalities(seq);
>          if (!mddev_get(mddev))
>                  return 0;
>
> @@ -8385,6 +8408,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
>          }
>          spin_unlock(&mddev->lock);
>          spin_lock(&all_mddevs_lock);
> +
> +       if (mddev == list_last_entry(&all_mddevs, struct mddev, all_mddevs))
> +               status_unused(seq);
> +
>          if (atomic_dec_and_test(&mddev->active))
>                  __mddev_put(mddev);
>

I think something like the following is the right way to do this.

Thanks,
Song

diff --git i/drivers/md/md.c w/drivers/md/md.c
index 38a6767c65b1..14044febe009 100644
--- i/drivers/md/md.c
+++ w/drivers/md/md.c
@@ -8215,20 +8215,8 @@ static int status_resync(struct seq_file *seq,
struct mddev *mddev)
 static void *md_seq_start(struct seq_file *seq, loff_t *pos)
        __acquires(&all_mddevs_lock)
 {
-       struct md_personality *pers;
-
-       seq_puts(seq, "Personalities : ");
-       spin_lock(&pers_lock);
-       list_for_each_entry(pers, &pers_list, list)
-               seq_printf(seq, "[%s] ", pers->name);
-
-       spin_unlock(&pers_lock);
-       seq_puts(seq, "\n");
-       seq->poll_event = atomic_read(&md_event_count);
-
        spin_lock(&all_mddevs_lock);
-
-       return seq_list_start(&all_mddevs, *pos);
+       return seq_list_start_head(&all_mddevs, *pos);
 }

 static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
@@ -8243,12 +8231,31 @@ static void md_seq_stop(struct seq_file *seq, void *v)
        spin_unlock(&all_mddevs_lock);
 }

+static void md_seq_print_header(struct seq_file *seq)
+{
+       struct md_personality *pers;
+
+       seq_puts(seq, "Personalities : ");
+       spin_lock(&pers_lock);
+       list_for_each_entry(pers, &pers_list, list)
+               seq_printf(seq, "[%s] ", pers->name);
+
+       spin_unlock(&pers_lock);
+       seq_puts(seq, "\n");
+       seq->poll_event = atomic_read(&md_event_count);
+}
+
 static int md_seq_show(struct seq_file *seq, void *v)
 {
        struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
        sector_t sectors;
        struct md_rdev *rdev;

+       if (v == &all_mddevs) {
+               md_seq_print_header(seq);
+               return 0;
+       }
+
        if (!mddev_get(mddev))
                return 0;

Re: [PATCH v3 2/2] md: simplify md_seq_ops

[Yu Kuai]

Hi,

在 2024/01/09 16:12, Song Liu 写道:
> On Mon, Jan 8, 2024 at 11:48 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>
>> Hi,
>>
>> 在 2024/01/09 9:21, Yu Kuai 写道:
>>> Hi,
>>>
>>> 在 2024/01/09 7:38, Song Liu 写道:
>>>> On Tue, Sep 26, 2023 at 11:19 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
> [...]
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index e351e6c51cc7..289d3d89e73d 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -8135,6 +8135,19 @@ static void status_unused(struct seq_file *seq)
>>           seq_printf(seq, "\n");
>>    }
>>
>> +static void status_personalities(struct seq_file *seq)
>> +{
>> +       struct md_personality *pers;
>> +
>> +       seq_puts(seq, "Personalities : ");
>> +       spin_lock(&pers_lock);
>> +       list_for_each_entry(pers, &pers_list, list)
>> +               seq_printf(seq, "[%s] ", pers->name);
>> +
>> +       spin_unlock(&pers_lock);
>> +       seq_puts(seq, "\n");
>> +}
>> +
>>    static int status_resync(struct seq_file *seq, struct mddev *mddev)
>>    {
>>           sector_t max_sectors, resync, res;
>> @@ -8273,43 +8286,53 @@ static int status_resync(struct seq_file *seq,
>> struct mddev *mddev)
>>           return 1;
>>    }
>>
>> +#define MDDEV_NONE (void *)1
>> +
>>    static void *md_seq_start(struct seq_file *seq, loff_t *pos)
>>           __acquires(&all_mddevs_lock)
>>    {
>> -       struct md_personality *pers;
>> -
>> -       seq_puts(seq, "Personalities : ");
>> -       spin_lock(&pers_lock);
>> -       list_for_each_entry(pers, &pers_list, list)
>> -               seq_printf(seq, "[%s] ", pers->name);
>> -
>> -       spin_unlock(&pers_lock);
>> -       seq_puts(seq, "\n");
>>           seq->poll_event = atomic_read(&md_event_count);
>> -
>>           spin_lock(&all_mddevs_lock);
>>
>> -       return seq_list_start(&all_mddevs, *pos);
>> +       if (!list_empty(&all_mddevs))
>> +               return seq_list_start(&all_mddevs, *pos);
>> +       else if (*pos == 0)
>> +               return MDDEV_NONE;
>> +       else
>> +               return NULL;
>>    }
>>
>>    static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
>>    {
>> +       if (v == MDDEV_NONE) {
>> +               ++*pos;
>> +               return NULL;
>> +       }
>> +
>>           return seq_list_next(v, &all_mddevs, pos);
>>    }
>>
>>    static void md_seq_stop(struct seq_file *seq, void *v)
>>           __releases(&all_mddevs_lock)
>>    {
>> -       status_unused(seq);
>>           spin_unlock(&all_mddevs_lock);
>>    }
>>    static int md_seq_show(struct seq_file *seq, void *v)
>>    {
>> -       struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
>> +       struct mddev *mddev;
>>           sector_t sectors;
>>           struct md_rdev *rdev;
>>
>> +       if (v == MDDEV_NONE) {
>> +               status_personalities(seq);
>> +               status_unused(seq);
>> +               return 0;
>> +       }
>> +
>> +       mddev = list_entry(v, struct mddev, all_mddevs);
>> +       if (mddev == list_first_entry(&all_mddevs, struct mddev,
>> all_mddevs))
>> +               status_personalities(seq);
>>           if (!mddev_get(mddev))
>>                   return 0;
>>
>> @@ -8385,6 +8408,10 @@ static int md_seq_show(struct seq_file *seq, void *v)
>>           }
>>           spin_unlock(&mddev->lock);
>>           spin_lock(&all_mddevs_lock);
>> +
>> +       if (mddev == list_last_entry(&all_mddevs, struct mddev, all_mddevs))
>> +               status_unused(seq);
>> +
>>           if (atomic_dec_and_test(&mddev->active))
>>                   __mddev_put(mddev);
>>
> 
> I think something like the following is the right way to do this.
> 
> Thanks,
> Song
> 
> diff --git i/drivers/md/md.c w/drivers/md/md.c
> index 38a6767c65b1..14044febe009 100644
> --- i/drivers/md/md.c
> +++ w/drivers/md/md.c
> @@ -8215,20 +8215,8 @@ static int status_resync(struct seq_file *seq,
> struct mddev *mddev)
>   static void *md_seq_start(struct seq_file *seq, loff_t *pos)
>          __acquires(&all_mddevs_lock)
>   {
> -       struct md_personality *pers;
> -
> -       seq_puts(seq, "Personalities : ");
> -       spin_lock(&pers_lock);
> -       list_for_each_entry(pers, &pers_list, list)
> -               seq_printf(seq, "[%s] ", pers->name);
> -
> -       spin_unlock(&pers_lock);
> -       seq_puts(seq, "\n");
> -       seq->poll_event = atomic_read(&md_event_count);
> -
>          spin_lock(&all_mddevs_lock);
> -
> -       return seq_list_start(&all_mddevs, *pos);
> +       return seq_list_start_head(&all_mddevs, *pos);

Yes, this is good. I didn't notice the api seq_list_start_head().
>   }
> 
>   static void *md_seq_next(struct seq_file *seq, void *v, loff_t *pos)
> @@ -8243,12 +8231,31 @@ static void md_seq_stop(struct seq_file *seq, void *v)
>          spin_unlock(&all_mddevs_lock);
>   }
> 
> +static void md_seq_print_header(struct seq_file *seq)
> +{
> +       struct md_personality *pers;
> +
> +       seq_puts(seq, "Personalities : ");
> +       spin_lock(&pers_lock);
> +       list_for_each_entry(pers, &pers_list, list)
> +               seq_printf(seq, "[%s] ", pers->name);
> +
> +       spin_unlock(&pers_lock);
> +       seq_puts(seq, "\n");
> +       seq->poll_event = atomic_read(&md_event_count);
> +}
> +
>   static int md_seq_show(struct seq_file *seq, void *v)
>   {
>          struct mddev *mddev = list_entry(v, struct mddev, all_mddevs);
>          sector_t sectors;
>          struct md_rdev *rdev;
> 
> +       if (v == &all_mddevs) {
> +               md_seq_print_header(seq);

And I will still move status_unused() to md_seq_show(), because 
seq_read_iter() only handle the case that seq_printf() overflowed from
md_seq_show(), not md_seq_start/stop().

Thanks,
Kuai

> +               return 0;
> +       }
> +
>          if (!mddev_get(mddev))
>                  return 0;
> 
> .
>