linux-kernel - Re: [PATCH 2/2] debugfs: log errors when something goes wrong

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Message-ID: <CAJZ5v0goKqHXfG=nNprMtKTDj02s3U56BOGQTuqajcqVdqqFcw@mail.gmail.com>
Date:   Wed, 3 Jul 2019 11:10:44 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mark Brown <broonie@...nel.org>, Takashi Iwai <tiwai@...e.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 2/2] debugfs: log errors when something goes wrong

On Wed, Jul 3, 2019 at 9:17 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> As it is not recommended that debugfs calls be checked, it was pointed
> out that major errors should still be logged somewhere so that
> developers and users have a chance to figure out what went wrong.  To
> help with this, error logging has been added to the debugfs core so that
> it is not needed to be present in every individual file that calls
> debugfs.
>
> Reported-by: Mark Brown <broonie@...nel.org>
> Reported-by: Takashi Iwai <tiwai@...e.de>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Generally speaking

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  fs/debugfs/inode.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> index f04c8475d9a1..7f43c8acfcbf 100644
> --- a/fs/debugfs/inode.c
> +++ b/fs/debugfs/inode.c
> @@ -2,8 +2,9 @@
>  /*
>   *  inode.c - part of debugfs, a tiny little debug file system
>   *
> - *  Copyright (C) 2004 Greg Kroah-Hartman <greg@...ah.com>
> + *  Copyright (C) 2004,2019 Greg Kroah-Hartman <greg@...ah.com>
>   *  Copyright (C) 2004 IBM Inc.
> + *  Copyright (C) 2019 Linux Foundation <gregkh@...uxfoundation.org>
>   *
>   *  debugfs is for people to use instead of /proc or /sys.
>   *  See ./Documentation/core-api/kernel-api.rst for more details.
> @@ -294,8 +295,10 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
>
>         error = simple_pin_fs(&debug_fs_type, &debugfs_mount,
>                               &debugfs_mount_count);
> -       if (error)
> +       if (error) {
> +               pr_err("Unable to pin filesystem for file '%s'\n", name);

But I'm not sure about the log level here.  Particularly, why would
pr_info() not work?

>                 return ERR_PTR(error);
> +       }
>
>         /* If the parent is not specified, we create it in the root.
>          * We need the root dentry to do this, which is in the super
> @@ -309,6 +312,7 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
>         dentry = lookup_one_len(name, parent, strlen(name));
>         if (!IS_ERR(dentry) && d_really_is_positive(dentry)) {
>                 dput(dentry);
> +               pr_err("File '%s' already present!\n", name);
>                 dentry = ERR_PTR(-EEXIST);
>         }
>
> @@ -351,8 +355,11 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
>                 return dentry;
>
>         inode = debugfs_get_inode(dentry->d_sb);
> -       if (unlikely(!inode))
> +       if (unlikely(!inode)) {
> +               pr_err("out of free dentries, can not create file '%s'\n",
> +                      name);
>                 return failed_creating(dentry);
> +       }
>
>         inode->i_mode = mode;
>         inode->i_private = data;
> @@ -513,8 +520,11 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
>                 return dentry;
>
>         inode = debugfs_get_inode(dentry->d_sb);
> -       if (unlikely(!inode))
> +       if (unlikely(!inode)) {
> +               pr_err("out of free dentries, can not create directory '%s'\n",
> +                      name);
>                 return failed_creating(dentry);
> +       }
>
>         inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
>         inode->i_op = &simple_dir_inode_operations;
> @@ -552,8 +562,11 @@ struct dentry *debugfs_create_automount(const char *name,
>                 return dentry;
>
>         inode = debugfs_get_inode(dentry->d_sb);
> -       if (unlikely(!inode))
> +       if (unlikely(!inode)) {
> +               pr_err("out of free dentries, can not create automount '%s'\n",
> +                      name);
>                 return failed_creating(dentry);
> +       }
>
>         make_empty_dir_inode(inode);
>         inode->i_flags |= S_AUTOMOUNT;
> @@ -608,6 +621,8 @@ struct dentry *debugfs_create_symlink(const char *name, struct dentry *parent,
>
>         inode = debugfs_get_inode(dentry->d_sb);
>         if (unlikely(!inode)) {
> +               pr_err("out of free dentries, can not create symlink '%s'\n",
> +                      name);
>                 kfree(link);
>                 return failed_creating(dentry);
>         }
> --
> 2.22.0
>