perf inject: Add facility to do in place update

When there is a need to modify only timestamps, it is much simpler and
quicker to do it to the existing file rather than re-write all the
contents.

In preparation for that, add the ability to modify the input file in place.
In practice that just means making the file descriptor and mmaps writable.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20210430070309.17624-5-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-inject.c

@@ -43,6 +43,8 @@ struct perf_inject {
 	bool			have_auxtrace;
 	bool			strip;
 	bool			jit_mode;
+	bool			in_place_update;
+	bool			in_place_update_dry_run;
 	const char		*input_name;
 	struct perf_data	output;
 	u64			bytes_written;
@@ -701,7 +703,7 @@ static int __cmd_inject(struct perf_inject *inject)
 	int ret = -EINVAL;
 	struct perf_session *session = inject->session;
 	struct perf_data *data_out = &inject->output;
-	int fd = perf_data__fd(data_out);
+	int fd = inject->in_place_update ? -1 : perf_data__fd(data_out);
 	u64 output_data_offset;
 
 	signal(SIGINT, sig_handler);
@@ -759,14 +761,14 @@ static int __cmd_inject(struct perf_inject *inject)
 	if (!inject->itrace_synth_opts.set)
 		auxtrace_index__free(&session->auxtrace_index);
 
-	if (!data_out->is_pipe)
+	if (!data_out->is_pipe && !inject->in_place_update)
 		lseek(fd, output_data_offset, SEEK_SET);
 
 	ret = perf_session__process_events(session);
 	if (ret)
 		return ret;
 
-	if (!data_out->is_pipe) {
+	if (!data_out->is_pipe && !inject->in_place_update) {
 		if (inject->build_ids)
 			perf_header__set_feat(&session->header,
 					      HEADER_BUILD_ID);
@@ -900,7 +902,23 @@ int cmd_inject(int argc, const char **argv)
 		return -1;
 	}
 
-	if (perf_data__open(&inject.output)) {
+	if (inject.in_place_update) {
+		if (!strcmp(inject.input_name, "-")) {
+			pr_err("Input file name required for in-place updating\n");
+			return -1;
+		}
+		if (strcmp(inject.output.path, "-")) {
+			pr_err("Output file name must not be specified for in-place updating\n");
+			return -1;
+		}
+		if (!data.force && !inject.in_place_update_dry_run) {
+			pr_err("The input file would be updated in place, "
+				"the --force option is required.\n");
+			return -1;
+		}
+		if (!inject.in_place_update_dry_run)
+			data.in_place_update = true;
+	} else if (perf_data__open(&inject.output)) {
 		perror("failed to create output file");
 		return -1;
 	}

tools/perf/util/data.c

@@ -240,11 +240,12 @@ static bool is_dir(struct perf_data *data)
 
 static int open_file_read(struct perf_data *data)
 {
+	int flags = data->in_place_update ? O_RDWR : O_RDONLY;
 	struct stat st;
 	int fd;
 	char sbuf[STRERR_BUFSIZE];
 
-	fd = open(data->file.path, O_RDONLY);
+	fd = open(data->file.path, flags);
 	if (fd < 0) {
 		int err = errno;
 

tools/perf/util/data.h

@@ -31,6 +31,7 @@ struct perf_data {
 	bool			 is_dir;
 	bool			 force;
 	bool			 use_stdio;
+	bool			 in_place_update;
 	enum perf_data_mode	 mode;
 
 	struct {

tools/perf/util/header.c

@@ -3814,6 +3814,11 @@ int perf_session__read_header(struct perf_session *session)
 	if (perf_file_header__read(&f_header, header, fd) < 0)
 		return -EINVAL;
 
+	if (header->needs_swap && data->in_place_update) {
+		pr_err("In-place update not supported when byte-swapping is required\n");
+		return -EINVAL;
+	}
+
 	/*
 	 * Sanity check that perf.data was written cleanly; data size is
 	 * initialized to 0 and updated only if the on_exit function is run.

tools/perf/util/session.c

@@ -2155,6 +2155,7 @@ struct reader {
 	u64		 data_size;
 	u64		 data_offset;
 	reader_cb_t	 process;
+	bool		 in_place_update;
 };
 
 static int
@@ -2188,7 +2189,9 @@ reader__process_events(struct reader *rd, struct perf_session *session,
 	mmap_prot  = PROT_READ;
 	mmap_flags = MAP_SHARED;
 
-	if (session->header.needs_swap) {
+	if (rd->in_place_update) {
+		mmap_prot  |= PROT_WRITE;
+	} else if (session->header.needs_swap) {
 		mmap_prot  |= PROT_WRITE;
 		mmap_flags = MAP_PRIVATE;
 	}
@@ -2274,6 +2277,7 @@ static int __perf_session__process_events(struct perf_session *session)
 		.data_size	= session->header.data_size,
 		.data_offset	= session->header.data_offset,
 		.process	= process_simple,
+		.in_place_update = session->data->in_place_update,
 	};
 	struct ordered_events *oe = &session->ordered_events;
 	struct perf_tool *tool = session->tool;