From dab2c6ee1f308af001dd4f57a13ec16e765f930b Mon Sep 17 00:00:00 2001 From: David Gibson Date: Fri, 24 Jun 2022 12:17:29 +1000 Subject: Add cleaner line-by-line reading primitives Two places in passt need to read files line by line (one parsing resolv.conf, the other parsing /proc/net/*. They can't use fgets() because in glibc that can allocate memory. Instead they use an implementation line_read() in util.c. This has some problems: * It has two completely separate modes of operation, one buffering and one not, the relation between these and how they're activated is subtle and confusing * At least in non-buffered mode, it will mishandle an empty line, folding them onto the start of the next non-empty line * In non-buffered mode it will use lseek() which prevents using this on non-regular files (we don't need that at present, but it's a surprising limitation) * It has a lot of difficult to read pointer mangling Add a new cleaner implementation of allocation-free line-by-line reading in lineread.c. This one always buffers, using a state structure to keep track of what we need. This is larger than I'd like, but it turns out handling all the edge cases of line-by-line reading in C is surprisingly hard. This just adds the code, subsequent patches will change the existing users of line_read() to the new implementation. Signed-off-by: David Gibson --- lineread.h | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) create mode 100644 lineread.h (limited to 'lineread.h') diff --git a/lineread.h b/lineread.h new file mode 100644 index 0000000..b6faff5 --- /dev/null +++ b/lineread.h @@ -0,0 +1,31 @@ +/* SPDX-License-Identifier: AGPL-3.0-or-later + * Copyright Red Hat + * Author: David Gibson + */ + +#ifndef LINEREAD_H +#define LINEREAD_H + +#define LINEREAD_BUFFER_SIZE 8192 + +/** + * struct lineread - Line reader state + * @fd: File descriptor lines are read from + * @next_line: Offset in @buf of the start of the first line not yet + * returned by lineread_get() + * @count: Number of bytes in @buf read from the file, but not yet + * returned by lineread_get() + * @buf: Buffer storing data read from file. + */ +struct lineread { + int fd; int next_line; + int count; + + /* One extra byte for possible trailing \0 */ + char buf[LINEREAD_BUFFER_SIZE+1]; +}; + +void lineread_init(struct lineread *lr, int fd); +int lineread_get(struct lineread *lr, char **line); + +#endif /* _LINEREAD_H */ -- cgit v1.2.3