[PATCH v1 3/7] tools lib subcmd: Add run_command_strbuf

[Ian Rogers]

Often a command wants to be run in a shell with stdout placed in a
string. This API mimics that of stdio's popen, running the given
command (not argv array) with "/bin/sh -c" then appending the output
from stdout to the buf argument.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/lib/subcmd/Makefile      | 32 +++++++++++++++++++++++++++++---
 tools/lib/subcmd/run-command.c | 30 ++++++++++++++++++++++++++++++
 tools/lib/subcmd/run-command.h | 14 ++++++++++++++
 3 files changed, 73 insertions(+), 3 deletions(-)

diff --git a/tools/lib/subcmd/Makefile b/tools/lib/subcmd/Makefile
index b87213263a5e..23174d013519 100644
--- a/tools/lib/subcmd/Makefile
+++ b/tools/lib/subcmd/Makefile
@@ -13,6 +13,7 @@ CC ?= $(CROSS_COMPILE)gcc
 LD ?= $(CROSS_COMPILE)ld
 AR ?= $(CROSS_COMPILE)ar
 
+MKDIR = mkdir
 RM = rm -f
 
 MAKEFLAGS += --no-print-directory
@@ -55,6 +56,17 @@ CFLAGS += -I$(srctree)/tools/include/
 
 CFLAGS += $(EXTRA_WARNINGS) $(EXTRA_CFLAGS)
 
+LIBAPI_DIR      = $(srctree)/tools/lib/api/
+ifneq ($(OUTPUT),)
+  LIBAPI_OUTPUT = $(abspath $(OUTPUT))/libapi
+else
+  LIBAPI_OUTPUT = $(CURDIR)/libapi
+endif
+LIBAPI_DESTDIR = $(LIBAPI_OUTPUT)
+LIBAPI_INCLUDE = $(LIBAPI_DESTDIR)/include
+LIBAPI = $(LIBAPI_OUTPUT)/libapi.a
+CFLAGS += -I$(LIBAPI_OUTPUT)/include
+
 SUBCMD_IN := $(OUTPUT)libsubcmd-in.o
 
 ifeq ($(LP64), 1)
@@ -76,7 +88,9 @@ include $(srctree)/tools/build/Makefile.include
 
 all: fixdep $(LIBFILE)
 
-$(SUBCMD_IN): FORCE
+prepare: $(LIBAPI)
+
+$(SUBCMD_IN): FORCE prepare
 	@$(MAKE) $(build)=libsubcmd
 
 $(LIBFILE): $(SUBCMD_IN)
@@ -113,10 +127,22 @@ install_headers: $(INSTALL_HDRS)
 
 install: install_lib install_headers
 
-clean:
+$(LIBAPI_OUTPUT):
+	$(Q)$(MKDIR) -p $@
+
+$(LIBAPI): FORCE | $(LIBAPI_OUTPUT)
+	$(Q)$(MAKE) -C $(LIBAPI_DIR) O=$(LIBAPI_OUTPUT) \
+		DESTDIR=$(LIBAPI_DESTDIR) prefix= \
+		$@ install_headers
+
+$(LIBAPI)-clean:
+	$(call QUIET_CLEAN, libapi)
+	$(Q)$(RM) -r -- $(LIBAPI_OUTPUT)
+
+clean: $(LIBAPI)-clean
 	$(call QUIET_CLEAN, libsubcmd) $(RM) $(LIBFILE); \
 	find $(or $(OUTPUT),.) -name \*.o -or -name \*.o.cmd -or -name \*.o.d | xargs $(RM)
 
 FORCE:
 
-.PHONY: clean FORCE
+.PHONY: clean FORCE prepare
diff --git a/tools/lib/subcmd/run-command.c b/tools/lib/subcmd/run-command.c
index 5cdac2162532..e90b285b6720 100644
--- a/tools/lib/subcmd/run-command.c
+++ b/tools/lib/subcmd/run-command.c
@@ -7,6 +7,7 @@
 #include <linux/string.h>
 #include <errno.h>
 #include <sys/wait.h>
+#include <api/strbuf.h>
 #include "subcmd-util.h"
 #include "run-command.h"
 #include "exec-cmd.h"
@@ -227,3 +228,32 @@ int run_command_v_opt(const char **argv, int opt)
 	prepare_run_command_v_opt(&cmd, argv, opt);
 	return run_command(&cmd);
 }
+
+int run_command_strbuf(const char *cmd, struct strbuf *buf)
+{
+	const char *argv[4] = {
+		"/bin/sh",
+		"-c",
+		cmd,
+		NULL
+	};
+	struct child_process child = {
+		.argv = argv,
+		.out = -1,
+	};
+	int err;
+	ssize_t read_sz;
+
+	err = start_command(&child);
+	if (err)
+		return err;
+
+	read_sz = strbuf_read(buf, child.out, 0);
+
+	err = finish_command(&child);
+	close(child.out);
+	if (read_sz < 0)
+		return (int)read_sz;
+
+	return err;
+}
diff --git a/tools/lib/subcmd/run-command.h b/tools/lib/subcmd/run-command.h
index 17d969c6add3..1f7a2af9248c 100644
--- a/tools/lib/subcmd/run-command.h
+++ b/tools/lib/subcmd/run-command.h
@@ -58,4 +58,18 @@ int run_command(struct child_process *);
 #define RUN_COMMAND_STDOUT_TO_STDERR 4
 int run_command_v_opt(const char **argv, int opt);
 
+struct strbuf;
+/**
+ * run_command_strbuf() - Run cmd using /bin/sh and place stdout in strbuf.
+ * @cmd: The command to run by "/bin/sh -c".
+ * @buf: The strbuf appended to by reading stdout.
+ *
+ * Similar to popen with fread, run the given command reading the stdout output
+ * to buf. As with popen, stderr output goes to the current processes stderr but
+ * may be redirected in cmd by using "2>&1".
+ *
+ * Return: 0 on success or a negative error code on failure.
+ */
+int run_command_strbuf(const char *cmd, struct strbuf *buf);
+
 #endif /* __SUBCMD_RUN_COMMAND_H */
-- 
2.39.0.314.g84b9a713c41-goog