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

Ian Rogers
2020-04-01T23:40:41Z

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.
+ */
+
+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;
+}
+
+/* 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