linux-kernel - Re: [PATCH v5 01/10] scsi: scsi_debug: create scsi_debug directory in the debugfs filesystem

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Message-ID: <8c7cfe09-d145-4387-91cf-da9d4e2398e1@interlog.com>
Date:   Wed, 27 Sep 2023 21:13:05 -0400
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     Wenchao Hao <haowenchao2@...wei.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        open-iscsi@...glegroups.com, linux-scsi@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, louhongxiang@...wei.com
Subject: Re: [PATCH v5 01/10] scsi: scsi_debug: create scsi_debug directory in
 the debugfs filesystem

On 2023-09-22 05:28, Wenchao Hao wrote:
> Create directory scsi_debug in the root of the debugfs filesystem.
> Prepare to add interface for manage error injection.
> 
> Acked-by: Douglas Gilbert <dgilbert@...erlog.com>
> Signed-off-by: Wenchao Hao <haowenchao2@...wei.com>
> ---
>   drivers/scsi/scsi_debug.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index 9c0af50501f9..35c336271b13 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -41,6 +41,7 @@
>   #include <linux/random.h>
>   #include <linux/xarray.h>
>   #include <linux/prefetch.h>
> +#include <linux/debugfs.h>
>   
>   #include <net/checksum.h>
>   
> @@ -862,6 +863,8 @@ static const int device_qfull_result =
>   
>   static const int condition_met_result = SAM_STAT_CONDITION_MET;
>   
> +static struct dentry *sdebug_debugfs_root;
> +
>   
>   /* Only do the extra work involved in logical block provisioning if one or
>    * more of the lbpu, lbpws or lbpws10 parameters are given and we are doing
> @@ -7011,6 +7014,8 @@ static int __init scsi_debug_init(void)
>   		goto driver_unreg;
>   	}
>   
> +	sdebug_debugfs_root = debugfs_create_dir("scsi_debug", NULL);

debugfs_create_dir() can fail and return NULL. Looking at other drivers, most
seem to assume it will work. Since the scsi_debug driver is often used to test
abnormal situations, perhaps adding something like:
     if (!sdebug_debugfs_root)
         pr_info("%s: failed to create initial debugfs directory\n", __func__);

might save someone a bit of time if a NULL dereference on sdebug_debugfs_root
follows later. That is what the mpt3sas driver does.

Doug Gilbert

> +
>   	for (k = 0; k < hosts_to_add; k++) {
>   		if (want_store && k == 0) {
>   			ret = sdebug_add_host_helper(idx);
> @@ -7057,6 +7062,7 @@ static void __exit scsi_debug_exit(void)
>   
>   	sdebug_erase_all_stores(false);
>   	xa_destroy(per_store_ap);
> +	debugfs_remove(sdebug_debugfs_root);
>   }
>   
>   device_initcall(scsi_debug_init);