linux-kernel - Re: [PATCH 4/5] tools api: add a lightweight buffered reading api

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Date:   Thu, 2 Apr 2020 15:41:37 +0200
From:   Jiri Olsa <jolsa@...hat.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Andrey Zhizhikin <andrey.z@...il.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 4/5] tools api: add a lightweight buffered reading api

On Wed, Apr 01, 2020 at 04:39:44PM -0700, Ian Rogers wrote:
> The synthesize benchmark shows the majority of execution time going to
> fgets and sscanf, necessary to parse /proc/pid/maps. Add a new buffered
> reading library that will be used to replace these calls in a follow-up
> CL.
> 
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/lib/api/io.h | 103 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 103 insertions(+)
>  create mode 100644 tools/lib/api/io.h
> 
> diff --git a/tools/lib/api/io.h b/tools/lib/api/io.h
> new file mode 100644
> index 000000000000..e88d76c59440
> --- /dev/null
> +++ b/tools/lib/api/io.h
> @@ -0,0 +1,103 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Lightweight buffered reading library.
> + *
> + * Copyright 2019 Google LLC.
> + */

missing the recursion header check

#ifndef __PERF_IO_H
#define __PERF_IO_H 

> +
> +struct io {
> +	/* File descriptor being read/ */
> +	int fd;
> +	/* Size of the read buffer. */
> +	unsigned int buf_len;
> +	/* Pointer to storage for buffering read. */
> +	char *buf;
> +	/* End of the storage. */
> +	char *end;
> +	/* Currently accessed data pointer. */
> +	char *data;
> +	/* Set true on when the end of file on read error. */
> +	bool eof;
> +};
> +
> +static inline void init_io(struct io *io, int fd,
> +			   char *buf, unsigned int buf_len)
> +{
> +	io->fd = fd;
> +	io->buf_len = buf_len;
> +	io->buf = buf;
> +	io->end = buf;
> +	io->data = buf;
> +	io->eof = false;
> +}

looks good, could you please add io__ prefix for all functions?

thanks,
jirka

> +
> +/* Reads one character from the "io" file with similar semantics to fgetc. */
> +static inline int get_char(struct io *io)
> +{
> +	char *ptr = io->data;
> +
> +	if (ptr == io->end) {
> +		ssize_t n = read(io->fd, io->buf, io->buf_len);
> +
> +		if (n <= 0) {
> +			io->eof = true;
> +			return -1;
> +		}
> +		ptr = &io->buf[0];
> +		io->end = &io->buf[n];
> +	}
> +	io->data = ptr + 1;
> +	return *ptr;
> +}
> +
> +/* Read a hexadecimal value with no 0x prefix into the out argument hex.
> + * Returns -1 on error or if nothing is read, otherwise returns the character
> + * after the hexadecimal value.
> + */
> +static inline int get_hex(struct io *io, __u64 *hex)
> +{
> +	bool first_read = true;
> +
> +	*hex = 0;
> +	while (true) {
> +		char ch = get_char(io);
> +
> +		if (ch < 0)
> +			return ch;
> +		if (ch >= '0' && ch <= '9')
> +			*hex = (*hex << 4) | (ch - '0');
> +		else if (ch >= 'a' && ch <= 'f')
> +			*hex = (*hex << 4) | (ch - 'a' + 10);
> +		else if (ch >= 'A' && ch <= 'F')
> +			*hex = (*hex << 4) | (ch - 'A' + 10);
> +		else if (first_read)
> +			return -1;
> +		else
> +			return ch;
> +		first_read = false;
> +	}
> +}
> +
> +/* Read a decimal value into the out argument dec.
> + * Returns -1 on error or if nothing is read, otherwise returns the character
> + * after the decimal value.
> + */
> +static inline int get_dec(struct io *io, __u64 *dec)
> +{
> +	bool first_read = true;
> +
> +	*dec = 0;
> +	while (true) {
> +		char ch = get_char(io);
> +
> +		if (ch < 0)
> +			return ch;
> +		if (ch >= '0' && ch <= '9')
> +			*dec = (*dec * 10) + ch - '0';
> +		else if (first_read)
> +			return -1;
> +		else
> +			return ch;
> +		first_read = false;
> +	}
> +}
> -- 
> 2.26.0.rc2.310.g2932bb562d-goog
>