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

Jiri Olsa
2020-04-02T13:41:51Z

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@google.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
>