dab2c6ee1f
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 <david@gibson.dropbear.id.au>
115 lines
2.7 KiB
C
115 lines
2.7 KiB
C
// SPDX-License-Identifier: AGPL-3.0-or-later
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/* PASST - Plug A Simple Socket Transport
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* for qemu/UNIX domain socket mode
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*
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* PASTA - Pack A Subtle Tap Abstraction
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* for network namespace/tap device mode
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*
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* lineread.c - Allocation free line-by-line buffered file input
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*
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* Copyright Red Hat
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* Author: David Gibson <david@gibson.dropbear.id.au>
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*/
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#include <stddef.h>
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#include <fcntl.h>
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#include <string.h>
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#include <stdbool.h>
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#include <assert.h>
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#include <unistd.h>
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#include "lineread.h"
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/**
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* lineread_init() - Prepare for line by line file reading without allocation
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* @lr: Line reader state structure to initialize
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* @fd: File descriptor to read lines from
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*/
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void lineread_init(struct lineread *lr, int fd)
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{
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lr->fd = fd;
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lr->next_line = lr->count = 0;
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}
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/**
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* peek_line() - Find and NULL-terminate next line in buffer
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* @lr: Line reader state structure
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* @eof: Caller indicates end-of-file was already found by read()
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*
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* Return: length of line in bytes, -1 if no line was found
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*/
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static int peek_line(struct lineread *lr, bool eof)
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{
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char *nl;
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/* Sanity checks (which also document invariants) */
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assert(lr->count >= 0);
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assert(lr->next_line >= 0);
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assert(lr->next_line + lr->count >= lr->next_line);
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assert(lr->next_line + lr->count <= LINEREAD_BUFFER_SIZE);
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nl = memchr(lr->buf + lr->next_line, '\n', lr->count);
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if (nl) {
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*nl = '\0';
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return nl - lr->buf - lr->next_line + 1;
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}
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if (eof) {
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lr->buf[lr->next_line + lr->count] = '\0';
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/* No trailing newline, so treat all remaining bytes
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* as the last line
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*/
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return lr->count;
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}
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return -1;
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}
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/**
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* lineread_get() - Read a single line from file (no allocation)
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* @lr: Line reader state structure
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* @line: Place a pointer to the next line in this variable
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*
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* Return: Length of line read on success, 0 on EOF, negative on error
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*/
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int lineread_get(struct lineread *lr, char **line)
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{
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bool eof = false;
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int line_len;
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while ((line_len = peek_line(lr, eof)) < 0) {
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int rc;
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if ((lr->next_line + lr->count) == LINEREAD_BUFFER_SIZE) {
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/* No space at end */
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if (lr->next_line == 0) {
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/* Buffer is full, which means we've
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* hit a line too long for us to
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* process. FIXME: report error
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* better
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*/
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return -1;
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}
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memmove(lr->buf, lr->buf + lr->next_line, lr->count);
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lr->next_line = 0;
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}
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/* Read more data into the end of buffer */
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rc = read(lr->fd, lr->buf + lr->next_line + lr->count,
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LINEREAD_BUFFER_SIZE - lr->next_line - lr->count);
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if (rc < 0)
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return rc;
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if (rc == 0)
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eof = true;
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else
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lr->count += rc;
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}
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*line = lr->buf + lr->next_line;
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lr->next_line += line_len;
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lr->count -= line_len;
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return line_len;
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}
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