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linux-stable/include/uapi/linux/netlink.h
Jakub Kicinski 5493a2ad0d docs: netlink: clarify the historical baggage of Netlink flags 
nlmsg_flags are full of historical baggage, inconsistencies and
strangeness. Try to document it more thoroughly. Explain the meaning
of the ECHO flag (and while at it clarify the comment in the uAPI).
Handwave a little about the NEW request flags and how they make
sense on the surface but cater to really old paradigm before commands
were a thing.

I will add more notes on how to make use of ECHO and discouragement
for reuse of flags to the kernel-side documentation.

Link: https://lore.kernel.org/r/20220927212306.823862-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2022-09-29 18:39:39 -07:00

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/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
#ifndef _UAPI__LINUX_NETLINK_H
#define _UAPI__LINUX_NETLINK_H
#include <linux/const.h>
#include <linux/socket.h> /* for __kernel_sa_family_t */
#include <linux/types.h>
#define NETLINK_ROUTE 0 /* Routing/device hook */
#define NETLINK_UNUSED 1 /* Unused number */
#define NETLINK_USERSOCK 2 /* Reserved for user mode socket protocols */
#define NETLINK_FIREWALL 3 /* Unused number, formerly ip_queue */
#define NETLINK_SOCK_DIAG 4 /* socket monitoring */
#define NETLINK_NFLOG 5 /* netfilter/iptables ULOG */
#define NETLINK_XFRM 6 /* ipsec */
#define NETLINK_SELINUX 7 /* SELinux event notifications */
#define NETLINK_ISCSI 8 /* Open-iSCSI */
#define NETLINK_AUDIT 9 /* auditing */
#define NETLINK_FIB_LOOKUP 10
#define NETLINK_CONNECTOR 11
#define NETLINK_NETFILTER 12 /* netfilter subsystem */
#define NETLINK_IP6_FW 13
#define NETLINK_DNRTMSG 14 /* DECnet routing messages (obsolete) */
#define NETLINK_KOBJECT_UEVENT 15 /* Kernel messages to userspace */
#define NETLINK_GENERIC 16
/* leave room for NETLINK_DM (DM Events) */
#define NETLINK_SCSITRANSPORT 18 /* SCSI Transports */
#define NETLINK_ECRYPTFS 19
#define NETLINK_RDMA 20
#define NETLINK_CRYPTO 21 /* Crypto layer */
#define NETLINK_SMC 22 /* SMC monitoring */
#define NETLINK_INET_DIAG NETLINK_SOCK_DIAG
#define MAX_LINKS 32
struct sockaddr_nl {
__kernel_sa_family_t nl_family; /* AF_NETLINK */
unsigned short nl_pad; /* zero */
__u32 nl_pid; /* port ID */
__u32 nl_groups; /* multicast groups mask */
};
/**
* struct nlmsghdr - fixed format metadata header of Netlink messages
* @nlmsg_len: Length of message including header
* @nlmsg_type: Message content type
* @nlmsg_flags: Additional flags
* @nlmsg_seq: Sequence number
* @nlmsg_pid: Sending process port ID
*/
struct nlmsghdr {
__u32 nlmsg_len;
__u16 nlmsg_type;
__u16 nlmsg_flags;
__u32 nlmsg_seq;
__u32 nlmsg_pid;
};
/* Flags values */
#define NLM_F_REQUEST 0x01 /* It is request message. */
#define NLM_F_MULTI 0x02 /* Multipart message, terminated by NLMSG_DONE */
#define NLM_F_ACK 0x04 /* Reply with ack, with zero or error code */
#define NLM_F_ECHO 0x08 /* Receive resulting notifications */
#define NLM_F_DUMP_INTR 0x10 /* Dump was inconsistent due to sequence change */
#define NLM_F_DUMP_FILTERED 0x20 /* Dump was filtered as requested */
/* Modifiers to GET request */
#define NLM_F_ROOT 0x100 /* specify tree root */
#define NLM_F_MATCH 0x200 /* return all matching */
#define NLM_F_ATOMIC 0x400 /* atomic GET */
#define NLM_F_DUMP (NLM_F_ROOT|NLM_F_MATCH)
/* Modifiers to NEW request */
#define NLM_F_REPLACE 0x100 /* Override existing */
#define NLM_F_EXCL 0x200 /* Do not touch, if it exists */
#define NLM_F_CREATE 0x400 /* Create, if it does not exist */
#define NLM_F_APPEND 0x800 /* Add to end of list */
/* Modifiers to DELETE request */
#define NLM_F_NONREC 0x100 /* Do not delete recursively */
#define NLM_F_BULK 0x200 /* Delete multiple objects */
/* Flags for ACK message */
#define NLM_F_CAPPED 0x100 /* request was capped */
#define NLM_F_ACK_TLVS 0x200 /* extended ACK TVLs were included */
/*
4.4BSD ADD NLM_F_CREATE|NLM_F_EXCL
4.4BSD CHANGE NLM_F_REPLACE
True CHANGE NLM_F_CREATE|NLM_F_REPLACE
Append NLM_F_CREATE
Check NLM_F_EXCL
*/
#define NLMSG_ALIGNTO 4U
#define NLMSG_ALIGN(len) ( ((len)+NLMSG_ALIGNTO-1) & ~(NLMSG_ALIGNTO-1) )
#define NLMSG_HDRLEN ((int) NLMSG_ALIGN(sizeof(struct nlmsghdr)))
#define NLMSG_LENGTH(len) ((len) + NLMSG_HDRLEN)
#define NLMSG_SPACE(len) NLMSG_ALIGN(NLMSG_LENGTH(len))
#define NLMSG_DATA(nlh) ((void *)(((char *)nlh) + NLMSG_HDRLEN))
#define NLMSG_NEXT(nlh,len) ((len) -= NLMSG_ALIGN((nlh)->nlmsg_len), \
(struct nlmsghdr *)(((char *)(nlh)) + \
NLMSG_ALIGN((nlh)->nlmsg_len)))
#define NLMSG_OK(nlh,len) ((len) >= (int)sizeof(struct nlmsghdr) && \
(nlh)->nlmsg_len >= sizeof(struct nlmsghdr) && \
(nlh)->nlmsg_len <= (len))
#define NLMSG_PAYLOAD(nlh,len) ((nlh)->nlmsg_len - NLMSG_SPACE((len)))
#define NLMSG_NOOP 0x1 /* Nothing. */
#define NLMSG_ERROR 0x2 /* Error */
#define NLMSG_DONE 0x3 /* End of a dump */
#define NLMSG_OVERRUN 0x4 /* Data lost */
#define NLMSG_MIN_TYPE 0x10 /* < 0x10: reserved control messages */
struct nlmsgerr {
int error;
struct nlmsghdr msg;
/*
* followed by the message contents unless NETLINK_CAP_ACK was set
* or the ACK indicates success (error == 0)
* message length is aligned with NLMSG_ALIGN()
*/
/*
* followed by TLVs defined in enum nlmsgerr_attrs
* if NETLINK_EXT_ACK was set
*/
};
/**
* enum nlmsgerr_attrs - nlmsgerr attributes
* @NLMSGERR_ATTR_UNUSED: unused
* @NLMSGERR_ATTR_MSG: error message string (string)
* @NLMSGERR_ATTR_OFFS: offset of the invalid attribute in the original
* message, counting from the beginning of the header (u32)
* @NLMSGERR_ATTR_COOKIE: arbitrary subsystem specific cookie to
* be used - in the success case - to identify a created
* object or operation or similar (binary)
* @NLMSGERR_ATTR_POLICY: policy for a rejected attribute
* @NLMSGERR_ATTR_MISS_TYPE: type of a missing required attribute,
* %NLMSGERR_ATTR_MISS_NEST will not be present if the attribute was
* missing at the message level
* @NLMSGERR_ATTR_MISS_NEST: offset of the nest where attribute was missing
* @__NLMSGERR_ATTR_MAX: number of attributes
* @NLMSGERR_ATTR_MAX: highest attribute number
*/
enum nlmsgerr_attrs {
NLMSGERR_ATTR_UNUSED,
NLMSGERR_ATTR_MSG,
NLMSGERR_ATTR_OFFS,
NLMSGERR_ATTR_COOKIE,
NLMSGERR_ATTR_POLICY,
NLMSGERR_ATTR_MISS_TYPE,
NLMSGERR_ATTR_MISS_NEST,
__NLMSGERR_ATTR_MAX,
NLMSGERR_ATTR_MAX = __NLMSGERR_ATTR_MAX - 1
};
#define NETLINK_ADD_MEMBERSHIP 1
#define NETLINK_DROP_MEMBERSHIP 2
#define NETLINK_PKTINFO 3
#define NETLINK_BROADCAST_ERROR 4
#define NETLINK_NO_ENOBUFS 5
#ifndef __KERNEL__
#define NETLINK_RX_RING 6
#define NETLINK_TX_RING 7
#endif
#define NETLINK_LISTEN_ALL_NSID 8
#define NETLINK_LIST_MEMBERSHIPS 9
#define NETLINK_CAP_ACK 10
#define NETLINK_EXT_ACK 11
#define NETLINK_GET_STRICT_CHK 12
struct nl_pktinfo {
__u32 group;
};
struct nl_mmap_req {
unsigned int nm_block_size;
unsigned int nm_block_nr;
unsigned int nm_frame_size;
unsigned int nm_frame_nr;
};
struct nl_mmap_hdr {
unsigned int nm_status;
unsigned int nm_len;
__u32 nm_group;
/* credentials */
__u32 nm_pid;
__u32 nm_uid;
__u32 nm_gid;
};
#ifndef __KERNEL__
enum nl_mmap_status {
NL_MMAP_STATUS_UNUSED,
NL_MMAP_STATUS_RESERVED,
NL_MMAP_STATUS_VALID,
NL_MMAP_STATUS_COPY,
NL_MMAP_STATUS_SKIP,
};
#define NL_MMAP_MSG_ALIGNMENT NLMSG_ALIGNTO
#define NL_MMAP_MSG_ALIGN(sz) __ALIGN_KERNEL(sz, NL_MMAP_MSG_ALIGNMENT)
#define NL_MMAP_HDRLEN NL_MMAP_MSG_ALIGN(sizeof(struct nl_mmap_hdr))
#endif
#define NET_MAJOR 36 /* Major 36 is reserved for networking */
enum {
NETLINK_UNCONNECTED = 0,
NETLINK_CONNECTED,
};
/*
* <------- NLA_HDRLEN ------> <-- NLA_ALIGN(payload)-->
* +---------------------+- - -+- - - - - - - - - -+- - -+
* | Header | Pad | Payload | Pad |
* | (struct nlattr) | ing | | ing |
* +---------------------+- - -+- - - - - - - - - -+- - -+
* <-------------- nlattr->nla_len -------------->
*/
struct nlattr {
__u16 nla_len;
__u16 nla_type;
};
/*
* nla_type (16 bits)
* +---+---+-------------------------------+
* | N | O | Attribute Type |
* +---+---+-------------------------------+
* N := Carries nested attributes
* O := Payload stored in network byte order
*
* Note: The N and O flag are mutually exclusive.
*/
#define NLA_F_NESTED (1 << 15)
#define NLA_F_NET_BYTEORDER (1 << 14)
#define NLA_TYPE_MASK ~(NLA_F_NESTED | NLA_F_NET_BYTEORDER)
#define NLA_ALIGNTO 4
#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 value is a bitmap that defines the values being set
* The selector is a bitmask that defines which value is legit
*
* Examples:
* value = 0x0, and selector = 0x1
* implies we are selecting bit 1 and we want to set its value to 0.
*
* value = 0x2, and selector = 0x2
* implies we are selecting bit 2 and we want to set its value to 1.
*
*/
struct nla_bitfield32 {
__u32 value;
__u32 selector;
};
/*
* policy descriptions - it's specific to each family how this is used
* Normally, it should be retrieved via a dump inside another attribute
* specifying where it applies.
*/
/**
* enum netlink_attribute_type - type of an attribute
* @NL_ATTR_TYPE_INVALID: unused
* @NL_ATTR_TYPE_FLAG: flag attribute (present/not present)
* @NL_ATTR_TYPE_U8: 8-bit unsigned attribute
* @NL_ATTR_TYPE_U16: 16-bit unsigned attribute
* @NL_ATTR_TYPE_U32: 32-bit unsigned attribute
* @NL_ATTR_TYPE_U64: 64-bit unsigned attribute
* @NL_ATTR_TYPE_S8: 8-bit signed attribute
* @NL_ATTR_TYPE_S16: 16-bit signed attribute
* @NL_ATTR_TYPE_S32: 32-bit signed attribute
* @NL_ATTR_TYPE_S64: 64-bit signed attribute
* @NL_ATTR_TYPE_BINARY: binary data, min/max length may be specified
* @NL_ATTR_TYPE_STRING: string, min/max length may be specified
* @NL_ATTR_TYPE_NUL_STRING: NUL-terminated string,
* min/max length may be specified
* @NL_ATTR_TYPE_NESTED: nested, i.e. the content of this attribute
* consists of sub-attributes. The nested policy and maxtype
* inside may be specified.
* @NL_ATTR_TYPE_NESTED_ARRAY: nested array, i.e. the content of this
* attribute contains sub-attributes whose type is irrelevant
* (just used to separate the array entries) and each such array
* entry has attributes again, the policy for those inner ones
* and the corresponding maxtype may be specified.
* @NL_ATTR_TYPE_BITFIELD32: &struct nla_bitfield32 attribute
*/
enum netlink_attribute_type {
NL_ATTR_TYPE_INVALID,
NL_ATTR_TYPE_FLAG,
NL_ATTR_TYPE_U8,
NL_ATTR_TYPE_U16,
NL_ATTR_TYPE_U32,
NL_ATTR_TYPE_U64,
NL_ATTR_TYPE_S8,
NL_ATTR_TYPE_S16,
NL_ATTR_TYPE_S32,
NL_ATTR_TYPE_S64,
NL_ATTR_TYPE_BINARY,
NL_ATTR_TYPE_STRING,
NL_ATTR_TYPE_NUL_STRING,
NL_ATTR_TYPE_NESTED,
NL_ATTR_TYPE_NESTED_ARRAY,
NL_ATTR_TYPE_BITFIELD32,
};
/**
* enum netlink_policy_type_attr - policy type attributes
* @NL_POLICY_TYPE_ATTR_UNSPEC: unused
* @NL_POLICY_TYPE_ATTR_TYPE: type of the attribute,
* &enum netlink_attribute_type (U32)
* @NL_POLICY_TYPE_ATTR_MIN_VALUE_S: minimum value for signed
* integers (S64)
* @NL_POLICY_TYPE_ATTR_MAX_VALUE_S: maximum value for signed
* integers (S64)
* @NL_POLICY_TYPE_ATTR_MIN_VALUE_U: minimum value for unsigned
* integers (U64)
* @NL_POLICY_TYPE_ATTR_MAX_VALUE_U: maximum value for unsigned
* integers (U64)
* @NL_POLICY_TYPE_ATTR_MIN_LENGTH: minimum length for binary
* attributes, no minimum if not given (U32)
* @NL_POLICY_TYPE_ATTR_MAX_LENGTH: maximum length for binary
* attributes, no maximum if not given (U32)
* @NL_POLICY_TYPE_ATTR_POLICY_IDX: sub policy for nested and
* nested array types (U32)
* @NL_POLICY_TYPE_ATTR_POLICY_MAXTYPE: maximum sub policy
* attribute for nested and nested array types, this can
* in theory be < the size of the policy pointed to by
* the index, if limited inside the nesting (U32)
* @NL_POLICY_TYPE_ATTR_BITFIELD32_MASK: valid mask for the
* bitfield32 type (U32)
* @NL_POLICY_TYPE_ATTR_MASK: mask of valid bits for unsigned integers (U64)
* @NL_POLICY_TYPE_ATTR_PAD: pad attribute for 64-bit alignment
*
* @__NL_POLICY_TYPE_ATTR_MAX: number of attributes
* @NL_POLICY_TYPE_ATTR_MAX: highest attribute number
*/
enum netlink_policy_type_attr {
NL_POLICY_TYPE_ATTR_UNSPEC,
NL_POLICY_TYPE_ATTR_TYPE,
NL_POLICY_TYPE_ATTR_MIN_VALUE_S,
NL_POLICY_TYPE_ATTR_MAX_VALUE_S,
NL_POLICY_TYPE_ATTR_MIN_VALUE_U,
NL_POLICY_TYPE_ATTR_MAX_VALUE_U,
NL_POLICY_TYPE_ATTR_MIN_LENGTH,
NL_POLICY_TYPE_ATTR_MAX_LENGTH,
NL_POLICY_TYPE_ATTR_POLICY_IDX,
NL_POLICY_TYPE_ATTR_POLICY_MAXTYPE,
NL_POLICY_TYPE_ATTR_BITFIELD32_MASK,
NL_POLICY_TYPE_ATTR_PAD,
NL_POLICY_TYPE_ATTR_MASK,
/* keep last */
__NL_POLICY_TYPE_ATTR_MAX,
NL_POLICY_TYPE_ATTR_MAX = __NL_POLICY_TYPE_ATTR_MAX - 1
};
#endif /* _UAPI__LINUX_NETLINK_H */
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