tools: bpftool: Document and add bash completion for -L, -B options

The -L|--use-loader option for using loader programs when loading, or
when generating a skeleton, did not have any documentation or bash
completion. Same thing goes for -B|--base-btf, used to pass a path to a
base BTF object for split BTF such as BTF for kernel modules.

This patch documents and adds bash completion for those options.

Fixes: 75fa1777694c ("tools/bpftool: Add bpftool support for split BTF")
Fixes: d510296d331a ("bpftool: Use syscall/loader program in "prog load" and "gen skeleton" command.")
Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210730215435.7095-7-quentin@isovalent.com

1 files changed, 47 insertions, 1 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-btf.rst b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
index 1d37f3809842..88b28aa7431f 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-btf.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-btf.rst
@@ -12,7 +12,8 @@ SYNOPSIS
 
 	**bpftool** [*OPTIONS*] **btf** *COMMAND*
 
-	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] | {**-d** | **--debug** } }
+	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] | {**-d** | **--debug** } |
+		{ **-B** | **--base-btf** } }
 
 	*COMMANDS* := { **dump** | **help** }
 
@@ -73,6 +74,20 @@ OPTIONS
 =======
 	.. include:: common_options.rst
 
+	-B, --base-btf *FILE*
+		  Pass a base BTF object. Base BTF objects are typically used
+		  with BTF objects for kernel modules. To avoid duplicating
+		  all kernel symbols required by modules, BTF objects for
+		  modules are "split", they are built incrementally on top of
+		  the kernel (vmlinux) BTF object. So the base BTF reference
+		  should usually point to the kernel BTF.
+
+		  When the main BTF object to process (for example, the
+		  module BTF to dump) is passed as a *FILE*, bpftool attempts
+		  to autodetect the path for the base object, and passing
+		  this option is optional. When the main BTF object is passed
+		  through other handles, this option becomes necessary.
+
 EXAMPLES
 ========
 **# bpftool btf dump id 1226**
@@ -217,3 +232,34 @@ All the standard ways to specify map or program are supported:
 **# bpftool btf dump prog tag b88e0a09b1d9759d**
 
 **# bpftool btf dump prog pinned /sys/fs/bpf/prog_name**
+
+|
+| **# bpftool btf dump file /sys/kernel/btf/i2c_smbus**
+| (or)
+| **# I2C_SMBUS_ID=$(bpftool btf show -p | jq '.[] | select(.name=="i2c_smbus").id')**
+| **# bpftool btf dump id ${I2C_SMBUS_ID} -B /sys/kernel/btf/vmlinux**
+
+::
+
+  [104848] STRUCT 'i2c_smbus_alert' size=40 vlen=2
+          'alert' type_id=393 bits_offset=0
+          'ara' type_id=56050 bits_offset=256
+  [104849] STRUCT 'alert_data' size=12 vlen=3
+          'addr' type_id=16 bits_offset=0
+          'type' type_id=56053 bits_offset=32
+          'data' type_id=7 bits_offset=64
+  [104850] PTR '(anon)' type_id=104848
+  [104851] PTR '(anon)' type_id=104849
+  [104852] FUNC 'i2c_register_spd' type_id=84745 linkage=static
+  [104853] FUNC 'smbalert_driver_init' type_id=1213 linkage=static
+  [104854] FUNC_PROTO '(anon)' ret_type_id=18 vlen=1
+          'ara' type_id=56050
+  [104855] FUNC 'i2c_handle_smbus_alert' type_id=104854 linkage=static
+  [104856] FUNC 'smbalert_remove' type_id=104854 linkage=static
+  [104857] FUNC_PROTO '(anon)' ret_type_id=18 vlen=2
+          'ara' type_id=56050
+          'id' type_id=56056
+  [104858] FUNC 'smbalert_probe' type_id=104857 linkage=static
+  [104859] FUNC 'smbalert_work' type_id=9695 linkage=static
+  [104860] FUNC 'smbus_alert' type_id=71367 linkage=static
+  [104861] FUNC 'smbus_do_alert' type_id=84827 linkage=static