bpf: Minor fixes to BPF helpers documentation

Minor improvements to the documentation for BPF helpers:

* Fix formatting for the description of "bpf_socket" for
  bpf_getsockopt() and bpf_setsockopt(), thus suppressing two warnings
  from rst2man about "Unexpected indentation".
* Fix formatting for return values for bpf_sk_assign() and seq_file
  helpers.
* Fix and harmonise formatting, in particular for function/struct names.
* Remove blank lines before "Return:" sections.
* Replace tabs found in the middle of text lines.
* Fix typos.
* Add a note to the footer (in Python script) about "bpftool feature
  probe", including for listing features available to unprivileged
  users, and add a reference to bpftool man page.

Thanks to Florian for reporting two typos (duplicated words).

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200511161536.29853-4-quentin@isovalent.com

2 files changed, 65 insertions, 50 deletions

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 9d1932e23cec..bfb31c1be219 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -675,8 +675,8 @@ union bpf_attr {
  * 		For tracing programs, safely attempt to read *size* bytes from
  * 		kernel space address *unsafe_ptr* and store the data in *dst*.
  *
- * 		Generally, use bpf_probe_read_user() or bpf_probe_read_kernel()
- * 		instead.
+ * 		Generally, use **bpf_probe_read_user**\ () or
+ * 		**bpf_probe_read_kernel**\ () instead.
  * 	Return
  * 		0 on success, or a negative error in case of failure.
  *
@@ -684,7 +684,7 @@ union bpf_attr {
  * 	Description
  * 		Return the time elapsed since system boot, in nanoseconds.
  * 		Does not include time the system was suspended.
- * 		See: clock_gettime(CLOCK_MONOTONIC)
+ * 		See: **clock_gettime**\ (**CLOCK_MONOTONIC**)
  * 	Return
  * 		Current *ktime*.
  *
@@ -1543,11 +1543,11 @@ union bpf_attr {
  * int bpf_probe_read_str(void *dst, u32 size, const void *unsafe_ptr)
  * 	Description
  * 		Copy a NUL terminated string from an unsafe kernel address
- * 		*unsafe_ptr* to *dst*. See bpf_probe_read_kernel_str() for
+ * 		*unsafe_ptr* to *dst*. See **bpf_probe_read_kernel_str**\ () for
  * 		more details.
  *
- * 		Generally, use bpf_probe_read_user_str() or bpf_probe_read_kernel_str()
- * 		instead.
+ * 		Generally, use **bpf_probe_read_user_str**\ () or
+ * 		**bpf_probe_read_kernel_str**\ () instead.
  * 	Return
  * 		On success, the strictly positive length of the string,
  * 		including the trailing NUL character. On error, a negative
@@ -1575,7 +1575,7 @@ union bpf_attr {
  *
  * u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)
  * 	Description
- * 		Equivalent to bpf_get_socket_cookie() helper that accepts
+ * 		Equivalent to **bpf_get_socket_cookie**\ () helper that accepts
  * 		*skb*, but gets socket from **struct bpf_sock_ops** context.
  * 	Return
  * 		A 8-byte long non-decreasing number.
@@ -1604,6 +1604,7 @@ union bpf_attr {
  * 		The option value of length *optlen* is pointed by *optval*.
  *
  * 		*bpf_socket* should be one of the following:
+ *
  * 		* **struct bpf_sock_ops** for **BPF_PROG_TYPE_SOCK_OPS**.
  * 		* **struct bpf_sock_addr** for **BPF_CGROUP_INET4_CONNECT**
  * 		  and **BPF_CGROUP_INET6_CONNECT**.
@@ -1672,12 +1673,12 @@ union bpf_attr {
  *
  * 		The lower two bits of *flags* are used as the return code if
  * 		the map lookup fails. This is so that the return value can be
- * 		one of the XDP program return codes up to XDP_TX, as chosen by
- * 		the caller. Any higher bits in the *flags* argument must be
+ * 		one of the XDP program return codes up to **XDP_TX**, as chosen
+ * 		by the caller. Any higher bits in the *flags* argument must be
  * 		unset.
  *
- * 		See also bpf_redirect(), which only supports redirecting to an
- * 		ifindex, but doesn't require a map to do so.
+ * 		See also **bpf_redirect**\ (), which only supports redirecting
+ * 		to an ifindex, but doesn't require a map to do so.
  * 	Return
  * 		**XDP_REDIRECT** on success, or the value of the two lower bits
  * 		of the *flags* argument on error.
@@ -1785,7 +1786,7 @@ union bpf_attr {
  * 		the time running for event since last normalization. The
  * 		enabled and running times are accumulated since the perf event
  * 		open. To achieve scaling factor between two invocations of an
- * 		eBPF program, users can can use CPU id as the key (which is
+ * 		eBPF program, users can use CPU id as the key (which is
  * 		typical for perf array usage model) to remember the previous
  * 		value and do the calculation inside the eBPF program.
  * 	Return
@@ -1812,6 +1813,7 @@ union bpf_attr {
  * 		*opval* and of length *optlen*.
  *
  * 		*bpf_socket* should be one of the following:
+ *
  * 		* **struct bpf_sock_ops** for **BPF_PROG_TYPE_SOCK_OPS**.
  * 		* **struct bpf_sock_addr** for **BPF_CGROUP_INET4_CONNECT**
  * 		  and **BPF_CGROUP_INET6_CONNECT**.
@@ -1833,7 +1835,7 @@ union bpf_attr {
  * 		The first argument is the context *regs* on which the kprobe
  * 		works.
  *
- * 		This helper works by setting setting the PC (program counter)
+ * 		This helper works by setting the PC (program counter)
  * 		to an override function which is run in place of the original
  * 		probed function. This means the probed function is not run at
  * 		all. The replacement function just returns with the required
@@ -2300,7 +2302,7 @@ union bpf_attr {
  *		**bpf_rc_keydown**\ () again with the same values, or calling
  *		**bpf_rc_repeat**\ ().
  *
- *		Some protocols include a toggle bit, in case the button	was
+ *		Some protocols include a toggle bit, in case the button was
  *		released and pressed again between consecutive scancodes.
  *
  *		The *ctx* should point to the lirc sample as passed into
@@ -2646,7 +2648,6 @@ union bpf_attr {
  *
  * 		*th* points to the start of the TCP header, while *th_len*
  * 		contains **sizeof**\ (**struct tcphdr**).
- *
  * 	Return
  * 		0 if *iph* and *th* are a valid SYN cookie ACK, or a negative
  * 		error otherwise.
@@ -2829,7 +2830,6 @@ union bpf_attr {
  *
  *		*th* points to the start of the TCP header, while *th_len*
  *		contains the length of the TCP header.
- *
  *	Return
  *		On success, lower 32 bits hold the generated SYN cookie in
  *		followed by 16 bits which hold the MSS value for that cookie,
@@ -2912,7 +2912,7 @@ union bpf_attr {
  * 				// size, after checking its boundaries.
  * 			}
  *
- * 		In comparison, using **bpf_probe_read_user()** helper here
+ * 		In comparison, using **bpf_probe_read_user**\ () helper here
  * 		instead to read the string would require to estimate the length
  * 		at compile time, and would often result in copying more memory
  * 		than necessary.
@@ -2930,14 +2930,14 @@ union bpf_attr {
  * int bpf_probe_read_kernel_str(void *dst, u32 size, const void *unsafe_ptr)
  * 	Description
  * 		Copy a NUL terminated string from an unsafe kernel address *unsafe_ptr*
- * 		to *dst*. Same semantics as with bpf_probe_read_user_str() apply.
+ * 		to *dst*. Same semantics as with **bpf_probe_read_user_str**\ () apply.
  * 	Return
- * 		On success, the strictly positive length of the string,	including
+ * 		On success, the strictly positive length of the string, including
  * 		the trailing NUL character. On error, a negative value.
  *
  * int bpf_tcp_send_ack(void *tp, u32 rcv_nxt)
  *	Description
- *		Send out a tcp-ack. *tp* is the in-kernel struct tcp_sock.
+ *		Send out a tcp-ack. *tp* is the in-kernel struct **tcp_sock**.
  *		*rcv_nxt* is the ack_seq to be sent out.
  *	Return
  *		0 on success, or a negative error in case of failure.
@@ -2965,19 +2965,19 @@ union bpf_attr {
  * int bpf_read_branch_records(struct bpf_perf_event_data *ctx, void *buf, u32 size, u64 flags)
  *	Description
  *		For an eBPF program attached to a perf event, retrieve the
- *		branch records (struct perf_branch_entry) associated to *ctx*
- *		and store it in	the buffer pointed by *buf* up to size
+ *		branch records (**struct perf_branch_entry**) associated to *ctx*
+ *		and store it in the buffer pointed by *buf* up to size
  *		*size* bytes.
  *	Return
  *		On success, number of bytes written to *buf*. On error, a
  *		negative value.
  *
  *		The *flags* can be set to **BPF_F_GET_BRANCH_RECORDS_SIZE** to
- *		instead	return the number of bytes required to store all the
+ *		instead return the number of bytes required to store all the
  *		branch entries. If this flag is set, *buf* may be NULL.
  *
  *		**-EINVAL** if arguments invalid or **size** not a multiple
- *		of sizeof(struct perf_branch_entry).
+ *		of **sizeof**\ (**struct perf_branch_entry**\ ).
  *
  *		**-ENOENT** if architecture does not support branch records.
  *
@@ -2985,8 +2985,8 @@ union bpf_attr {
  *	Description
  *		Returns 0 on success, values for *pid* and *tgid* as seen from the current
  *		*namespace* will be returned in *nsdata*.
- *
- *		On failure, the returned value is one of the following:
+ *	Return
+ *		0 on success, or one of the following in case of failure:
  *
  *		**-EINVAL** if dev and inum supplied don't match dev_t and inode number
  *              with nsfs of current task, or if dev conversion to dev_t lost high bits.
@@ -3025,8 +3025,8 @@ union bpf_attr {
  * 		a global identifier that can be assumed unique. If *ctx* is
  * 		NULL, then the helper returns the cookie for the initial
  * 		network namespace. The cookie itself is very similar to that
- * 		of bpf_get_socket_cookie() helper, but for network namespaces
- * 		instead of sockets.
+ * 		of **bpf_get_socket_cookie**\ () helper, but for network
+ * 		namespaces instead of sockets.
  * 	Return
  * 		A 8-byte long opaque number.
  *
@@ -3061,57 +3061,66 @@ union bpf_attr {
  *
  *		The *flags* argument must be zero.
  *	Return
- *		0 on success, or a negative errno in case of failure.
+ *		0 on success, or a negative error in case of failure:
  *
- *		* **-EINVAL**		Unsupported flags specified.
- *		* **-ENOENT**		Socket is unavailable for assignment.
- *		* **-ENETUNREACH**	Socket is unreachable (wrong netns).
- *		* **-EOPNOTSUPP**	Unsupported operation, for example a
- *					call from outside of TC ingress.
- *		* **-ESOCKTNOSUPPORT**	Socket type not supported (reuseport).
+ *		**-EINVAL** if specified *flags* are not supported.
+ *
+ *		**-ENOENT** if the socket is unavailable for assignment.
+ *
+ *		**-ENETUNREACH** if the socket is unreachable (wrong netns).
+ *
+ *		**-EOPNOTSUPP** if the operation is not supported, for example
+ *		a call from outside of TC ingress.
+ *
+ *		**-ESOCKTNOSUPPORT** if the socket type is not supported
+ *		(reuseport).
  *
  * u64 bpf_ktime_get_boot_ns(void)
  * 	Description
  * 		Return the time elapsed since system boot, in nanoseconds.
  * 		Does include the time the system was suspended.
- * 		See: clock_gettime(CLOCK_BOOTTIME)
+ * 		See: **clock_gettime**\ (**CLOCK_BOOTTIME**)
  * 	Return
  * 		Current *ktime*.
  *
  * int bpf_seq_printf(struct seq_file *m, const char *fmt, u32 fmt_size, const void *data, u32 data_len)
  * 	Description
- * 		seq_printf uses seq_file seq_printf() to print out the format string.
+ * 		**bpf_seq_printf**\ () uses seq_file **seq_printf**\ () to print
+ * 		out the format string.
  * 		The *m* represents the seq_file. The *fmt* and *fmt_size* are for
  * 		the format string itself. The *data* and *data_len* are format string
- * 		arguments. The *data* are a u64 array and corresponding format string
+ * 		arguments. The *data* are a **u64** array and corresponding format string
  * 		values are stored in the array. For strings and pointers where pointees
  * 		are accessed, only the pointer values are stored in the *data* array.
- * 		The *data_len* is the *data* size in term of bytes.
+ * 		The *data_len* is the size of *data* in bytes.
  *
  *		Formats **%s**, **%p{i,I}{4,6}** requires to read kernel memory.
  *		Reading kernel memory may fail due to either invalid address or
  *		valid address but requiring a major memory fault. If reading kernel memory
  *		fails, the string for **%s** will be an empty string, and the ip
  *		address for **%p{i,I}{4,6}** will be 0. Not returning error to
- *		bpf program is consistent with what bpf_trace_printk() does for now.
+ *		bpf program is consistent with what **bpf_trace_printk**\ () does for now.
  * 	Return
- * 		0 on success, or a negative errno in case of failure.
+ * 		0 on success, or a negative error in case of failure:
+ *
+ *		**-EBUSY** if per-CPU memory copy buffer is busy, can try again
+ *		by returning 1 from bpf program.
+ *
+ *		**-EINVAL** if arguments are invalid, or if *fmt* is invalid/unsupported.
+ *
+ *		**-E2BIG** if *fmt* contains too many format specifiers.
  *
- *		* **-EBUSY**		Percpu memory copy buffer is busy, can try again
- *					by returning 1 from bpf program.
- *		* **-EINVAL**		Invalid arguments, or invalid/unsupported formats.
- *		* **-E2BIG**		Too many format specifiers.
- *		* **-EOVERFLOW**	Overflow happens, the same object will be tried again.
+ *		**-EOVERFLOW** if an overflow happened: The same object will be tried again.
  *
  * int bpf_seq_write(struct seq_file *m, const void *data, u32 len)
  * 	Description
- * 		seq_write uses seq_file seq_write() to write the data.
+ * 		**bpf_seq_write**\ () uses seq_file **seq_write**\ () to write the data.
  * 		The *m* represents the seq_file. The *data* and *len* represent the
- *		data to write in bytes.
+ * 		data to write in bytes.
  * 	Return
- * 		0 on success, or a negative errno in case of failure.
+ * 		0 on success, or a negative error in case of failure:
  *
- *		* **-EOVERFLOW**	Overflow happens, the same object will be tried again.
+ *		**-EOVERFLOW** if an overflow happened: The same object will be tried again.
  */
 #define __BPF_FUNC_MAPPER(FN)		\
 	FN(unspec),			\
diff --git a/scripts/bpf_helpers_doc.py b/scripts/bpf_helpers_doc.py
index ded304c96a05..91fa668fa860 100755
--- a/scripts/bpf_helpers_doc.py
+++ b/scripts/bpf_helpers_doc.py
@@ -318,6 +318,11 @@ may be interested in:
   of eBPF maps are used with a given helper function.
 * *kernel/bpf/* directory contains other files in which additional helpers are
   defined (for cgroups, sockmaps, etc.).
+* The bpftool utility can be used to probe the availability of helper functions
+  on the system (as well as supported program and map types, and a number of
+  other parameters). To do so, run **bpftool feature probe** (see
+  **bpftool-feature**\ (8) for details). Add the **unprivileged** keyword to
+  list features available to unprivileged users.
 
 Compatibility between helper functions and program types can generally be found
 in the files where helper functions are defined. Look for the **struct
@@ -338,6 +343,7 @@ SEE ALSO
 ========
 
 **bpf**\ (2),
+**bpftool**\ (8),
 **cgroups**\ (7),
 **ip**\ (8),
 **perf_event_open**\ (2),