Messages in this thread | | | From | Namhyung Kim <> | Date | Sat, 4 Apr 2020 12:06:45 +0900 | Subject | Re: [PATCH v2 4/5] tools api: add a lightweight buffered reading api |
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Hello,
On Fri, Apr 3, 2020 at 12:44 AM Ian Rogers <irogers@google.com> 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 | 107 +++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 107 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..5aa5b0e26a7a > --- /dev/null > +++ b/tools/lib/api/io.h > @@ -0,0 +1,107 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +/* > + * Lightweight buffered reading library. > + * > + * Copyright 2019 Google LLC. > + */ > +#ifndef __API_IO__ > +#define __API_IO__ > + > +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 io__init(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; > +} > + > +/* Reads one character from the "io" file with similar semantics to fgetc. */ > +static inline int io__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 io__get_hex(struct io *io, __u64 *hex) > +{ > + bool first_read = true; > + > + *hex = 0; > + while (true) { > + char ch = io__get_char(io); > +
Maybe you can add this
if (io->eof) return 0;
Please see below
> + 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; > + } > +}
What if a file contains hex digits at the end (without trailing spaces)? I guess it'd see EOF and return -1, right?
And it'd better to be clear when it sees a big hex numbers - it could have a comment that it'd simply discard upper bits or return an error.
> + > +/* 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 io__get_dec(struct io *io, __u64 *dec) > +{ > + bool first_read = true; > + > + *dec = 0; > + while (true) { > + char ch = io__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; > + } > +}
Ditto.
Thanks Namhyung
> + > +#endif /* __API_IO__ */ > -- > 2.26.0.rc2.310.g2932bb562d-goog >
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