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: 75fa1777 ("tools/bpftool: Add bpftool support for split BTF")
Fixes: d510296d ("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

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

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**

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

tools/bpf/bpftool/bash-completion/bpftool

@@ -260,7 +260,8 @@ _bpftool()
 
     # Deal with options
     if [[ ${words[cword]} == -* ]]; then
-        local c='--version --json --pretty --bpffs --mapcompat --debug'
+        local c='--version --json --pretty --bpffs --mapcompat --debug \
+	       --use-loader --base-btf'
         COMPREPLY=( $( compgen -W "$c" -- "$cur" ) )
         return 0
     fi
@@ -278,7 +279,7 @@ _bpftool()
             _sysfs_get_netdevs
             return 0
             ;;
-        file|pinned)
+        file|pinned|-B|--base-btf)
             _filedir
             return 0
             ;;
@@ -291,7 +292,8 @@ _bpftool()
     # Remove all options so completions don't have to deal with them.
     local i
     for (( i=1; i < ${#words[@]}; )); do
-        if [[ ${words[i]::1} == - ]]; then
+        if [[ ${words[i]::1} == - ]] &&
+            [[ ${words[i]} != "-B" ]] && [[ ${words[i]} != "--base-btf" ]]; then
             words=( "${words[@]:0:i}" "${words[@]:i+1}" )
             [[ $i -le $cword ]] && cword=$(( cword - 1 ))
         else

tools/bpf/bpftool/btf.c

@@ -981,7 +981,8 @@ static int do_help(int argc, char **argv)
 		"       FORMAT  := { raw | c }\n"
 		"       " HELP_SPEC_MAP "\n"
 		"       " HELP_SPEC_PROGRAM "\n"
-		"       " HELP_SPEC_OPTIONS " }\n"
+		"       " HELP_SPEC_OPTIONS " |\n"
+		"                    {-B|--base-btf} }\n"
 		"",
 		bin_name, "btf");
 

tools/bpf/bpftool/cgroup.c

@@ -502,7 +502,7 @@ static int do_help(int argc, char **argv)
 		"       " HELP_SPEC_ATTACH_FLAGS "\n"
 		"       " HELP_SPEC_PROGRAM "\n"
 		"       " HELP_SPEC_OPTIONS " |\n"
-		"                    {-f|--bpffs} }
+		"                    {-f|--bpffs} }\n"
 		"",
 		bin_name, argv[-2]);
 

tools/bpf/bpftool/gen.c

@@ -1026,7 +1026,8 @@ static int do_help(int argc, char **argv)
 		"       %1$s %2$s skeleton FILE [name OBJECT_NAME]\n"
 		"       %1$s %2$s help\n"
 		"\n"
-		"       " HELP_SPEC_OPTIONS " }\n"
+		"       " HELP_SPEC_OPTIONS " |\n"
+		"                    {-L|--use-loader} }\n"
 		"",
 		bin_name, "gen");
 

tools/bpf/bpftool/prog.c

@@ -2260,7 +2260,8 @@ static int do_help(int argc, char **argv)
 		"                        stream_parser | flow_dissector }\n"
 		"       METRIC := { cycles | instructions | l1d_loads | llc_misses | itlb_misses | dtlb_misses }\n"
 		"       " HELP_SPEC_OPTIONS " |\n"
-		"                    {-f|--bpffs} | {-m|--mapcompat} | {-n|--nomount} }\n"
+		"                    {-f|--bpffs} | {-m|--mapcompat} | {-n|--nomount} |\n"
+		"                    {-L|--use-loader} }\n"
 		"",
 		bin_name, argv[-2]);