mirror of
https://passt.top/passt
synced 2024-12-22 21:55:22 +00:00
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>
116 lines
2.7 KiB
C
116 lines
2.7 KiB
C
// SPDX-License-Identifier: AGPL-3.0-or-later
|
|
|
|
/* PASST - Plug A Simple Socket Transport
|
|
* for qemu/UNIX domain socket mode
|
|
*
|
|
* PASTA - Pack A Subtle Tap Abstraction
|
|
* for network namespace/tap device mode
|
|
*
|
|
* lineread.c - Allocation free line-by-line buffered file input
|
|
*
|
|
* Copyright Red Hat
|
|
* Author: David Gibson <david@gibson.dropbear.id.au>
|
|
*/
|
|
|
|
#include <stddef.h>
|
|
#include <fcntl.h>
|
|
#include <string.h>
|
|
#include <stdbool.h>
|
|
#include <assert.h>
|
|
#include <unistd.h>
|
|
|
|
#include "lineread.h"
|
|
|
|
/**
|
|
* lineread_init() - Prepare for line by line file reading without allocation
|
|
* @lr: Line reader state structure to initialize
|
|
* @fd: File descriptor to read lines from
|
|
*/
|
|
void lineread_init(struct lineread *lr, int fd)
|
|
{
|
|
lr->fd = fd;
|
|
lr->next_line = lr->count = 0;
|
|
}
|
|
|
|
/**
|
|
* peek_line() - Find and NULL-terminate next line in buffer
|
|
* @lr: Line reader state structure
|
|
* @eof: Caller indicates end-of-file was already found by read()
|
|
*
|
|
* Return: length of line in bytes, -1 if no line was found
|
|
*/
|
|
static int peek_line(struct lineread *lr, bool eof)
|
|
{
|
|
char *nl;
|
|
|
|
/* Sanity checks (which also document invariants) */
|
|
assert(lr->count >= 0);
|
|
assert(lr->next_line >= 0);
|
|
assert(lr->next_line + lr->count >= lr->next_line);
|
|
assert(lr->next_line + lr->count <= LINEREAD_BUFFER_SIZE);
|
|
|
|
nl = memchr(lr->buf + lr->next_line, '\n', lr->count);
|
|
|
|
if (nl) {
|
|
*nl = '\0';
|
|
return nl - lr->buf - lr->next_line + 1;
|
|
}
|
|
|
|
if (eof) {
|
|
lr->buf[lr->next_line + lr->count] = '\0';
|
|
/* No trailing newline, so treat all remaining bytes
|
|
* as the last line
|
|
*/
|
|
return lr->count;
|
|
}
|
|
|
|
return -1;
|
|
}
|
|
|
|
/**
|
|
* lineread_get() - Read a single line from file (no allocation)
|
|
* @lr: Line reader state structure
|
|
* @line: Place a pointer to the next line in this variable
|
|
*
|
|
* Return: Length of line read on success, 0 on EOF, negative on error
|
|
*/
|
|
int lineread_get(struct lineread *lr, char **line)
|
|
{
|
|
bool eof = false;
|
|
int line_len;
|
|
|
|
while ((line_len = peek_line(lr, eof)) < 0) {
|
|
int rc;
|
|
|
|
if ((lr->next_line + lr->count) == LINEREAD_BUFFER_SIZE) {
|
|
/* No space at end */
|
|
if (lr->next_line == 0) {
|
|
/* Buffer is full, which means we've
|
|
* hit a line too long for us to
|
|
* process. FIXME: report error
|
|
* better
|
|
*/
|
|
return -1;
|
|
}
|
|
memmove(lr->buf, lr->buf + lr->next_line, lr->count);
|
|
lr->next_line = 0;
|
|
}
|
|
|
|
/* Read more data into the end of buffer */
|
|
rc = read(lr->fd, lr->buf + lr->next_line + lr->count,
|
|
LINEREAD_BUFFER_SIZE - lr->next_line - lr->count);
|
|
if (rc < 0)
|
|
return rc;
|
|
|
|
if (rc == 0)
|
|
eof = true;
|
|
else
|
|
lr->count += rc;
|
|
}
|
|
|
|
*line = lr->buf + lr->next_line;
|
|
lr->next_line += line_len;
|
|
lr->count -= line_len;
|
|
return line_len;
|
|
}
|