linux-kernel - Re: [PATCH v1 1/1] powerpc/papr_scm: Properly handle UUID types and API

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Message-ID: <af677216-82b4-f1fa-1d90-3d32dabf8583@linux.ibm.com>
Date:   Fri, 16 Apr 2021 13:28:21 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Vaibhav Jain <vaibhav@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        "Oliver O'Halloran" <oohall@...il.com>
Subject: Re: [PATCH v1 1/1] powerpc/papr_scm: Properly handle UUID types and
 API

On 4/15/21 7:16 PM, Andy Shevchenko wrote:
> Parse to and export from UUID own type, before dereferencing.
> This also fixes wrong comment (Little Endian UUID is something else)
> and should fix Sparse warnings about assigning strict types to POD.
> 
> Fixes: 43001c52b603 ("powerpc/papr_scm: Use ibm,unit-guid as the iset cookie")
> Fixes: 259a948c4ba1 ("powerpc/pseries/scm: Use a specific endian format for storing uuid from the device tree")
> Cc: Oliver O'Halloran <oohall@...il.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.ibm.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
> Not tested
>   arch/powerpc/platforms/pseries/papr_scm.c | 13 ++++++++-----
>   1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/papr_scm.c b/arch/powerpc/platforms/pseries/papr_scm.c
> index ae6f5d80d5ce..4366e1902890 100644
> --- a/arch/powerpc/platforms/pseries/papr_scm.c
> +++ b/arch/powerpc/platforms/pseries/papr_scm.c
> @@ -1085,8 +1085,9 @@ static int papr_scm_probe(struct platform_device *pdev)
>   	u32 drc_index, metadata_size;
>   	u64 blocks, block_size;
>   	struct papr_scm_priv *p;
> +	u8 uuid_raw[UUID_SIZE];
>   	const char *uuid_str;
> -	u64 uuid[2];
> +	uuid_t uuid;
>   	int rc;
>   
>   	/* check we have all the required DT properties */
> @@ -1129,16 +1130,18 @@ static int papr_scm_probe(struct platform_device *pdev)
>   	p->hcall_flush_required = of_property_read_bool(dn, "ibm,hcall-flush-required");
>   
>   	/* We just need to ensure that set cookies are unique across */
> -	uuid_parse(uuid_str, (uuid_t *) uuid);
> +	uuid_parse(uuid_str, &uuid);
> +
>   	/*
>   	 * cookie1 and cookie2 are not really little endian
> -	 * we store a little endian representation of the
> +	 * we store a raw buffer representation of the
>   	 * uuid str so that we can compare this with the label
>   	 * area cookie irrespective of the endian config with which
>   	 * the kernel is built.
>   	 */
> -	p->nd_set.cookie1 = cpu_to_le64(uuid[0]);
> -	p->nd_set.cookie2 = cpu_to_le64(uuid[1]);
> +	export_uuid(uuid_raw, &uuid);
> +	p->nd_set.cookie1 = get_unaligned_le64(&uuid_raw[0]);
> +	p->nd_set.cookie2 = get_unaligned_le64(&uuid_raw[8]);
>   

ok that does the equivalent of cpu_to_le64 there. So we are good. But 
the comment update is missing the details why we did that 
get_unaligned_le64. Maybe raw buffer representation is the correct term?
Should we add an example in the comment. ie,

/*
  * Historically we stored the cookie in the below format.
for a uuid str 72511b67-0b3b-42fd-8d1d-5be3cae8bcaa
cookie1 was  0xfd423b0b671b5172 cookie2 was 0xaabce8cae35b1d8d
*/



>   	/* might be zero */
>   	p->metadata_size = metadata_size;
>