netdev - Re: [PATCH net-next v11 1/4] net netlink: Add new type NLA_BITFIELD

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Date:   Tue, 25 Jul 2017 07:14:59 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        xiyou.wangcong@...il.com, dsahern@...il.com,
        eric.dumazet@...il.com, mrv@...atatu.com,
        simon.horman@...ronome.com, alex.aring@...il.com
Subject: Re: [PATCH net-next v11 1/4] net netlink: Add new type
 NLA_BITFIELD_32

On 17-07-24 07:14 AM, Jiri Pirko wrote:
> Mon, Jul 24, 2017 at 03:35:43AM CEST, jhs@...atatu.com wrote:
>> From: Jamal Hadi Salim <jhs@...atatu.com>
>>
>> Generic bitflags attribute content sent to the kernel by user.
>> With this type the user can either set or unset a flag in the
>> kernel.
>>
>> The nla_value is a bitmap that defines the values being set
>> The nla_selector is a bitmask that defines which value is legit.
>>
>> A check is made to ensure the rules that a kernel subsystem always
>> conforms to bitflags the kernel already knows about. i.e
>> if the user tries to set a bit flag that is not understood then
>> the _it will be rejected_.
>>
>> In the most basic form, the user specifies the attribute policy as:
>> [ATTR_GOO] = { .type = NLA_BITFIELD_32, .validation_data = &myvalidflags },
>>
>> where myvalidflags is the bit mask of the flags the kernel understands.
>>
>> If the user _does not_ provide myvalidflags then the attribute will
>> also be rejected.
>>
>> Examples:
>> nla_value = 0x0, and nla_selector = 0x1
>> implies we are selecting bit 1 and we want to set its value to 0.
>>
>> nla_value = 0x2, and nla_selector = 0x2
>> implies we are selecting bit 2 and we want to set its value to 1.
>>
>> Signed-off-by: Jamal Hadi Salim <jhs@...atatu.com>
>> ---
>> include/net/netlink.h        |  4 ++++
>> include/uapi/linux/netlink.h | 17 +++++++++++++++++
>> lib/nlattr.c                 | 21 +++++++++++++++++++++
>> 3 files changed, 42 insertions(+)
>>
>> diff --git a/include/net/netlink.h b/include/net/netlink.h
>> index ef8e6c3..e33d1fb 100644
>> --- a/include/net/netlink.h
>> +++ b/include/net/netlink.h
>> @@ -178,6 +178,7 @@ enum {
>> 	NLA_S16,
>> 	NLA_S32,
>> 	NLA_S64,
>> +	NLA_BITFIELD_32,
>> 	__NLA_TYPE_MAX,
>> };
>>
>> @@ -206,6 +207,7 @@ enum {
>>   *    NLA_MSECS            Leaving the length field zero will verify the
>>   *                         given type fits, using it verifies minimum length
>>   *                         just like "All other"
>> + *    NLA_BITFIELD_32      A 32-bit bitmap/bitselector attribute
>>   *    All other            Minimum length of attribute payload
>>   *
>>   * Example:
>> @@ -213,11 +215,13 @@ enum {
>>   * 	[ATTR_FOO] = { .type = NLA_U16 },
>>   *	[ATTR_BAR] = { .type = NLA_STRING, .len = BARSIZ },
>>   *	[ATTR_BAZ] = { .len = sizeof(struct mystruct) },
>> + *	[ATTR_GOO] = { .type = NLA_BITFIELD_32, .validation_data = &myvalidflags },
>>   * };
>>   */
>> struct nla_policy {
>> 	u16		type;
>> 	u16		len;
>> +	void            *validation_data;
>> };
>>
>> /**
>> diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
>> index f86127a..0ac05a6 100644
>> --- a/include/uapi/linux/netlink.h
>> +++ b/include/uapi/linux/netlink.h
>> @@ -226,5 +226,22 @@ struct nlattr {
>> #define NLA_ALIGN(len)		(((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1))
>> #define NLA_HDRLEN		((int) NLA_ALIGN(sizeof(struct nlattr)))
>>
>> +/* Generic 32 bitflags attribute content sent to the kernel.
>> + *
>> + * The nla_value is a bitmap that defines the values being set
>> + * The nla_selector is a bitmask that defines which value is legit
>> + *
>> + * Examples:
>> + *  nla_value = 0x0, and nla_selector = 0x1
>> + *  implies we are selecting bit 1 and we want to set its value to 0.
>> + *
>> + *  nla_value = 0x2, and nla_selector = 0x2
>> + *  implies we are selecting bit 2 and we want to set its value to 1.
>> + *
>> + */
>> +struct nla_bitfield_32 {
>> +	__u32 nla_value;
>> +	__u32 nla_selector;
> 
> I would just have "value" and "selector" here. "nla_" prefix indicates
> netlink attrubute, like in struct nlattr - nla_type, nla_len,
> and that is wrong indication.
> 

Sure ;->

> 
> 
>> +};
>>
>> #endif /* _UAPI__LINUX_NETLINK_H */
>> diff --git a/lib/nlattr.c b/lib/nlattr.c
>> index fb52435..c8aad7e 100644
>> --- a/lib/nlattr.c
>> +++ b/lib/nlattr.c
>> @@ -27,6 +27,20 @@
>> 	[NLA_S64]	= sizeof(s64),
>> };
>>
>> +static int validate_nla_bitfield_32(const struct nlattr *nla, void *valid_data)
> 
> This should be:
> static int validate_nla_bitfield_32(const struct nlattr *nla, u32 *valid_flags_allowed)
> 
> 
> Other than this 2 nits, this looks good.
> 
> 

Are you sure Jiri? ;->

cheers,
jamal