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

3 files changed, 84 insertions, 3 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
diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
index 709b93fe1da3..2ef2f2df0279 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-gen.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
@@ -12,7 +12,8 @@ SYNOPSIS
 
 	**bpftool** [*OPTIONS*] **gen** *COMMAND*
 
-	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] | { **-d** | **--debug** } }
+	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] | { **-d** | **--debug** } |
+		{ **-L** | **--use-loader** } }
 
 	*COMMAND* := { **object** | **skeleton** | **help** }
 
@@ -152,6 +153,12 @@ OPTIONS
 =======
 	.. include:: common_options.rst
 
+	-L, --use-loader
+		  For skeletons, generate a "light" skeleton (also known as "loader"
+		  skeleton). A light skeleton contains a loader eBPF program. It does
+		  not use the majority of the libbpf infrastructure, and does not need
+		  libelf.
+
 EXAMPLES
 ========
 **$ cat example1.bpf.c**
diff --git a/tools/bpf/bpftool/Documentation/bpftool-prog.rst b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
index 4b8412fe2c60..2ea5df30ff21 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-prog.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-prog.rst
@@ -13,7 +13,8 @@ SYNOPSIS
 	**bpftool** [*OPTIONS*] **prog** *COMMAND*
 
 	*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] | { **-d** | **--debug** } |
-		{ **-f** | **--bpffs** } | { **-m** | **--mapcompat** } | { **-n** | **--nomount** } }
+		{ **-f** | **--bpffs** } | { **-m** | **--mapcompat** } | { **-n** | **--nomount** } |
+		{ **-L** | **--use-loader** } }
 
 	*COMMANDS* :=
 	{ **show** | **list** | **dump xlated** | **dump jited** | **pin** | **load**
@@ -224,6 +225,20 @@ OPTIONS
 		  Do not automatically attempt to mount any virtual file system
 		  (such as tracefs or BPF virtual file system) when necessary.
 
+	-L, --use-loader
+		  Load program as a "loader" program. This is useful to debug
+		  the generation of such programs. When this option is in
+		  use, bpftool attempts to load the programs from the object
+		  file into the kernel, but does not pin them (therefore, the
+		  *PATH* must not be provided).
+
+		  When combined with the **-d**\ \|\ **--debug** option,
+		  additional debug messages are generated, and the execution
+		  of the loader program will use the **bpf_trace_printk**\ ()
+		  helper to log each step of loading BTF, creating the maps,
+		  and loading the programs (see **bpftool prog tracelog** as
+		  a way to dump those messages).
+
 EXAMPLES
 ========
 **# bpftool prog show**
@@ -327,3 +342,16 @@ EXAMPLES
       40176203 cycles                                                 (83.05%)
       42518139 instructions    #   1.06 insns per cycle               (83.39%)
            123 llc_misses      #   2.89 LLC misses per million insns  (83.15%)
+
+|
+| Output below is for the trace logs.
+| Run in separate terminals:
+| **# bpftool prog tracelog**
+| **# bpftool prog load -L -d file.o**
+
+::
+
+    bpftool-620059  [004] d... 2634685.517903: bpf_trace_printk: btf_load size 665 r=5
+    bpftool-620059  [004] d... 2634685.517912: bpf_trace_printk: map_create sample_map idx 0 type 2 value_size 4 value_btf_id 0 r=6
+    bpftool-620059  [004] d... 2634685.517997: bpf_trace_printk: prog_load sample insn_cnt 13 r=7
+    bpftool-620059  [004] d... 2634685.517999: bpf_trace_printk: close(5) = 0