[RFC PATCH 1/6] btrfs-progs: splitcmd-gen.sh: create btrfs-<subcommand> binaries for selected subcommands

[Axel Burri <axel@tty0.ch>]

Create separate binaries for each subcommand ("btrfs foo bar").
Least invasive approach, generate c-files for each command:

    # ./splitcmd-gen.sh
    # make V=1 btrfs-subvolume-show
    # make V=1 btrfs-send
    # [...]

Alternative approach: instead of including the c-file, link with obj
in Makefile, e.g.:

    btrfs_subvolume_show_objects = cmds-subvolume.o
    btrfs_send_objects = cmds-send.o
    [...]

This implies adaptions in cmds-subvolume.c (and others):

    -static int cmd_filesystem_show(int argc, char **argv)
    +int cmd_filesystem_show(int argc, char **argv)

If they are defined non-static, we could probably simplify further and
add `-Wl,-eentry` flags (changing entry point from "main" to "entry").

With this, and if handle_command_group() was declared in some library
instead of btrfs.c, we would get rid of generated files completely.

Signed-off-by: Axel Burri <axel@tty0.ch>
---
 splitcmd-gen.sh | 70 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 splitcmd.c.in   | 17 ++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100755 splitcmd-gen.sh
 create mode 100644 splitcmd.c.in

diff --git a/splitcmd-gen.sh b/splitcmd-gen.sh
new file mode 100755
index 00000000..4d2e0509
--- /dev/null
+++ b/splitcmd-gen.sh
@@ -0,0 +1,70 @@
+#!/bin/bash
+
+#
+# Generate c-files for btrfs subcommands defined below
+#
+
+# Notes on linux capabilities:
+#
+# btrfs-subvolume-show, btrfs-subvolume-list, btrfs-send:
+#  - CAP_FOWNER is only needed for O_NOATIME flag in open() system calls
+#  - why CAP_SYS_ADMIN? shouldn't CAP_DAC_READ_SEARCH be enough?
+#
+# btrfs-receive:
+#  - dependent on send-stream (see cmds-receive.c: "send_ops"):
+#    CAP_CHOWN, CAP_MKNOD, CAP_SETFCAP (for "lsetxattr")
+#
+# btrfs-filesystem-usage:
+#  - CAP_SYS_ADMIN is for BTRFS_IOC_TREE_SEARCH and BTRFS_IOC_FS_INFO
+#    in order to provide full level of detail, see btrfs-filesystem(8)
+
+
+makefile_out="Makefile.install_setcap"
+
+splitcmd_list=""
+setcap_lines=""
+
+function gen_splitcmd {
+    local name="$1"
+    local dest="${1}.c"
+    local cfile="$2"
+    local entry="$3"
+    local caps="$4"
+    echo "generating: ${dest} (cfile=${cfile}, entry=${entry})"
+    echo -e "/*\n * ${name}\n *\n * GENERATED BY splitcmd-gen.sh\n */\n" > $dest
+    sed -e "s|@BTRFS_SPLITCMD_CFILE_INCLUDE@|${cfile}|g" \
+        -e "s|@BTRFS_SPLITCMD_ENTRY@|${entry}|g" \
+        splitcmd.c.in >> $dest
+}
+
+gen_splitcmd "btrfs-subvolume-show" \
+             "cmds-subvolume.c" "cmd_subvol_show" \
+             "cap_sys_admin,cap_fowner,cap_dac_read_search"
+
+gen_splitcmd "btrfs-subvolume-list" \
+             "cmds-subvolume.c" "cmd_subvol_list" \
+             "cap_sys_admin,cap_fowner,cap_dac_read_search"
+
+gen_splitcmd "btrfs-subvolume-snapshot" \
+             "cmds-subvolume.c" "cmd_subvol_snapshot" \
+             "cap_sys_admin,cap_fowner,cap_dac_override,cap_dac_read_search"
+
+gen_splitcmd "btrfs-subvolume-delete" \
+             "cmds-subvolume.c" "cmd_subvol_delete" \
+             "cap_sys_admin,cap_dac_override"
+
+gen_splitcmd "btrfs-send" \
+             "cmds-send.c" "cmd_send" \
+             "cap_sys_admin,cap_fowner,cap_dac_read_search"
+
+gen_splitcmd "btrfs-receive" \
+             "cmds-receive.c" "cmd_receive" \
+             "cap_sys_admin,cap_fowner,cap_chown,cap_mknod,cap_setfcap,cap_dac_override,cap_dac_read_search"
+
+gen_splitcmd "btrfs-filesystem-usage" \
+             "cmds-fi-usage.c" "cmd_filesystem_usage" \
+             "cap_sys_admin"
+
+gen_splitcmd "btrfs-qgroup-destroy" \
+             "cmds-qgroup.c" "cmd_qgroup_destroy" \
+             "cap_sys_admin,cap_dac_override"
diff --git a/splitcmd.c.in b/splitcmd.c.in
new file mode 100644
index 00000000..aa07af9a
--- /dev/null
+++ b/splitcmd.c.in
@@ -0,0 +1,17 @@
+#include "@BTRFS_SPLITCMD_CFILE_INCLUDE@"
+
+/*
+ * Dummy object: used from second-level command groups (e.g. in
+ * "cmds-subvolume.c"), is never called in splitcmd executables.
+ */
+int handle_command_group(const struct cmd_group *grp, int argc,
+			 char **argv)
+{
+	exit(1);
+}
+
+
+int main(int argc, char **argv)
+{
+	return @BTRFS_SPLITCMD_ENTRY@(argc, argv);
+}
-- 
2.16.4