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Date:   Thu, 29 Apr 2021 11:31:54 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Adrian Hunter <adrian.hunter@intel.com>
Cc:     Jiri Olsa <jolsa@redhat.com>, Andi Kleen <ak@linux.intel.com>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 04/12] perf inject: Add facility to do in place update
Message-ID: <YIrDWjIYxwkxV5Xk@kernel.org>
References: <20210429125854.13905-1-adrian.hunter@intel.com>
 <20210429125854.13905-5-adrian.hunter@intel.com>
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Em Thu, Apr 29, 2021 at 03:58:46PM +0300, Adrian Hunter escreveu:
> 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.

Clever, and you took care of checking that the constraints are met, and
I see this paves the way for the actual 'perf inject' option that uses
this new 'perf inject' mode.

- Arnaldo
 
> Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
> ---
>  tools/perf/builtin-inject.c | 30 ++++++++++++++++++++++++++----
>  tools/perf/util/data.c      |  3 ++-
>  tools/perf/util/data.h      |  1 +
>  tools/perf/util/header.c    |  5 +++++
>  tools/perf/util/session.c   |  6 +++++-
>  5 files changed, 39 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index ddccc0eb7390..ddfdeb85c586 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/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 +902,27 @@ 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) {
> +			char reply[10];
> +
> +			printf("The input file will be updated in place. OK? (y/n) ");
> +			if (!fgets(reply, sizeof(reply), stdin) || strcmp(reply, "y\n")) {
> +				pr_err("Aborted\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;
>  	}
> diff --git a/tools/perf/util/data.c b/tools/perf/util/data.c
> index f29af4fc3d09..209fe63d4e49 100644
> --- a/tools/perf/util/data.c
> +++ b/tools/perf/util/data.c
> @@ -239,11 +239,12 @@ 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;
>  
> diff --git a/tools/perf/util/data.h b/tools/perf/util/data.h
> index 62a3e66fbee8..c9de82af5584 100644
> --- a/tools/perf/util/data.h
> +++ b/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 {
> diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
> index aa1e42518d37..02b13c7a23be 100644
> --- a/tools/perf/util/header.c
> +++ b/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.
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index eba3769be3f1..edd068ea8a6c 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -2131,6 +2131,7 @@ struct reader {
>  	u64		 data_size;
>  	u64		 data_offset;
>  	reader_cb_t	 process;
> +	bool		 in_place_update;
>  };
>  
>  static int
> @@ -2164,7 +2165,9 @@ 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;
>  	}
> @@ -2250,6 +2253,7 @@ 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;
> -- 
> 2.17.1
> 

-- 

- Arnaldo