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From:   Daeho Jeong <daeho43@gmail.com>
Date:   Wed, 1 Jul 2020 16:04:52 +0900
Message-ID: <CACOAw_wQx5wjdWDX_WFebNS42t=wBuSh_k7oQ4v7abBv80SZXw@mail.gmail.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: add symbolic link to kobject in sysfs
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
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Actually, I want to keep the mount number remaining to the same
number, even if it's re-mounted.
Or we need to keep track of the number being increased whenever it's
remounted. :(

2020=EB=85=84 7=EC=9B=94 1=EC=9D=BC (=EC=88=98) =EC=98=A4=ED=9B=84 3:36, Ch=
ao Yu <yuchao0@huawei.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> Hi Daeho,
>
> On 2020/6/30 8:56, Daeho Jeong wrote:
> > From: Daeho Jeong <daehojeong@google.com>
> >
> > Added a symbolic link to directory of sysfs. It will
> > create a symbolic link such as "mount_0" and "mount_1" to
> > each f2fs mount in the order of mounting filesystem. It will
> > provide easy access to sysfs node even if not knowing the
> > specific device node name like sda19 and dm-3.
>
> Just out of curiosity, if we mount/umount as below:
>
> mount /dev/zram0 /mnt/f2fs0
> mount /dev/zram1 /mnt/f2fs1
> umount /mnt/f2fs0
> mount /dev/zram0 /mnt/f2fs0
>
> Shouldn't sysfs structure be:
> mount_2 -> zram0
> mount_1 -> zram1
> zram0
> zram1
>
> Then we can know zram0 is mounted after zram1?
>
> However the result shows:
> mount_0 -> zram0
> mount_1 -> zram1
> zram0
> zram1
>
> Thanks,
>
> >
> > Signed-off-by: Daeho Jeong <daehojeong@google.com>
> > ---
> >  fs/f2fs/f2fs.h  |  4 ++++
> >  fs/f2fs/sysfs.c | 31 +++++++++++++++++++++++++++----
> >  2 files changed, 31 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 4b28fd42fdbc..7d6c5f8ce16b 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1419,6 +1419,8 @@ struct decompress_io_ctx {
> >  #define MAX_COMPRESS_LOG_SIZE                8
> >  #define MAX_COMPRESS_WINDOW_SIZE     ((PAGE_SIZE) << MAX_COMPRESS_LOG_=
SIZE)
> >
> > +#define MOUNT_NAME_SIZE                      20
> > +
> >  struct f2fs_sb_info {
> >       struct super_block *sb;                 /* pointer to VFS super b=
lock */
> >       struct proc_dir_entry *s_proc;          /* proc entry */
> > @@ -1599,6 +1601,8 @@ struct f2fs_sb_info {
> >       /* For sysfs suppport */
> >       struct kobject s_kobj;
> >       struct completion s_kobj_unregister;
> > +     int s_mount_id;
> > +     char s_mount_name[MOUNT_NAME_SIZE];
> >
> >       /* For shrinker support */
> >       struct list_head s_list;
> > diff --git a/fs/f2fs/sysfs.c b/fs/f2fs/sysfs.c
> > index ab40e1f89f23..64bbe0b3b830 100644
> > --- a/fs/f2fs/sysfs.c
> > +++ b/fs/f2fs/sysfs.c
> > @@ -18,6 +18,7 @@
> >  #include <trace/events/f2fs.h>
> >
> >  static struct proc_dir_entry *f2fs_proc_root;
> > +static struct ida f2fs_mount_ida;
> >
> >  /* Sysfs support for f2fs */
> >  enum {
> > @@ -906,6 +907,9 @@ int __init f2fs_init_sysfs(void)
> >       } else {
> >               f2fs_proc_root =3D proc_mkdir("fs/f2fs", NULL);
> >       }
> > +
> > +     ida_init(&f2fs_mount_ida);
> > +
> >       return ret;
> >  }
> >
> > @@ -915,6 +919,7 @@ void f2fs_exit_sysfs(void)
> >       kset_unregister(&f2fs_kset);
> >       remove_proc_entry("fs/f2fs", NULL);
> >       f2fs_proc_root =3D NULL;
> > +     ida_destroy(&f2fs_mount_ida);
> >  }
> >
> >  int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
> > @@ -926,12 +931,22 @@ int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
> >       init_completion(&sbi->s_kobj_unregister);
> >       err =3D kobject_init_and_add(&sbi->s_kobj, &f2fs_sb_ktype, NULL,
> >                               "%s", sb->s_id);
> > -     if (err) {
> > -             kobject_put(&sbi->s_kobj);
> > -             wait_for_completion(&sbi->s_kobj_unregister);
> > -             return err;
> > +     if (err)
> > +             goto err1;
> > +
> > +     sbi->s_mount_id =3D ida_simple_get(&f2fs_mount_ida, 0, 0, GFP_KER=
NEL);
> > +     if (sbi->s_mount_id < 0) {
> > +             err =3D sbi->s_mount_id;
> > +             goto err1;
> >       }
> >
> > +     snprintf(sbi->s_mount_name, MOUNT_NAME_SIZE, "mount_%d",
> > +                     sbi->s_mount_id);
> > +     err =3D sysfs_create_link(&f2fs_kset.kobj, &sbi->s_kobj,
> > +                     sbi->s_mount_name);
> > +     if (err)
> > +             goto err2;
> > +
> >       if (f2fs_proc_root)
> >               sbi->s_proc =3D proc_mkdir(sb->s_id, f2fs_proc_root);
> >
> > @@ -946,6 +961,12 @@ int f2fs_register_sysfs(struct f2fs_sb_info *sbi)
> >                               victim_bits_seq_show, sb);
> >       }
> >       return 0;
> > +err2:
> > +     ida_simple_remove(&f2fs_mount_ida, sbi->s_mount_id);
> > +err1:
> > +     kobject_put(&sbi->s_kobj);
> > +     wait_for_completion(&sbi->s_kobj_unregister);
> > +     return err;
> >  }
> >
> >  void f2fs_unregister_sysfs(struct f2fs_sb_info *sbi)
> > @@ -957,6 +978,8 @@ void f2fs_unregister_sysfs(struct f2fs_sb_info *sbi=
)
> >               remove_proc_entry("victim_bits", sbi->s_proc);
> >               remove_proc_entry(sbi->sb->s_id, f2fs_proc_root);
> >       }
> > +     sysfs_remove_link(&f2fs_kset.kobj, sbi->s_mount_name);
> > +     ida_simple_remove(&f2fs_mount_ida, sbi->s_mount_id);
> >       kobject_del(&sbi->s_kobj);
> >       kobject_put(&sbi->s_kobj);
> >  }
> >