abuild/abuild-fetch.c
Natanael Copa 3da770ce35 abuild-fetch: simplify and fix locking
Simplify locking by using lockf(3). It is POSIX compatible and should
work over NFS.

Fix download race condition when:
1) host A creates lockfile and aquire lock to fetch from distfiles
   mirror
2) host B opens the lockfile and waits for lock
3) host A gets 404 from distfiles, releases lock and deletes the
   lockfile, which host A has an open file handle for
4) host B gets lock of the deleted file and downloads file
5) host A retries download and creates a new lockfile, but is not
   blocked by host B, even if it should

Solve this by releaseing the lock, give the other processes a chance
to aquire it (using sleep(0)), and then only delete the lockfile if:
a) download was successful (no 404) or b) no-one else has a lock.

This reverts commit 281720ec39 (abuild-fetch: aquire a second lock
using flock(2))

fixes #10026
2021-05-06 13:03:14 +02:00

251 lines
5.6 KiB
C

/* MIT license
Copyright (C) 2015 Natanael Copa <ncopa@alpinelinux.org>
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
#include <sys/file.h>
#include <sys/wait.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
static char *program;
static char lockfile[PATH_MAX] = "";
struct cmdarray {
size_t argc;
char *argv[32];
};
void add_opt(struct cmdarray *cmd, char *opt)
{
cmd->argv[cmd->argc++] = opt;
cmd->argv[cmd->argc] = NULL;
}
int usage(int eval)
{
printf("usage: %s [-hk] [-d DESTDIR] URL\n", program);
return eval;
}
int fork_exec(char *argv[], int showerr)
{
int r = 202;
int status = 0;
pid_t childpid = fork();
if (childpid < 0 )
err(200, "fork");
if (childpid == 0) {
execvp(argv[0], argv);
if (showerr)
warn("%s", argv[0]);
_exit(201);
}
/* wait for curl/wget and get the exit code */
wait(&status);
if (WIFEXITED(status))
r = WEXITSTATUS(status);
return r;
}
static int aquire_lock(const char *lockfile)
{
int lockfd = open(lockfile, O_WRONLY|O_CREAT, 0660);
if (lockfd < 0)
err(1, "%s", lockfile);
if (lockf(lockfd, F_LOCK, 0) == -1)
err(1, "failed to aquire lock: %s", lockfile);
return lockfd;
}
static void release_lock(int lockfd)
{
if (lockf(lockfd, F_ULOCK, 0) == -1)
err(1, "failed to release lock");
}
static int try_lock(int lockfd)
{
return lockf(lockfd, F_TLOCK, 0) == 0;
}
/* create or wait for an NFS-safe lockfile and fetch url with curl or wget */
int fetch(char *url, const char *destdir, bool insecure)
{
int lockfd, status=0;
char outfile[PATH_MAX-5], partfile[PATH_MAX];
char *name, *p;
struct cmdarray curlcmd = {
.argc = 5,
.argv = { "curl", "-L", "-f", "-o", partfile, NULL }
};
struct cmdarray wgetcmd = {
.argc = 3,
.argv = { "wget", "-O", partfile, NULL }
};
name = strrchr(url, '/');
if (name == NULL)
errx(1, "%s: no '/' in url", url);
p = strstr(url, "::");
if (p != NULL) {
name = url;
*p = '\0';
url = p + 2;
} else {
name++;
}
snprintf(outfile, sizeof(outfile), "%s/%s", destdir, name);
snprintf(lockfile, sizeof(lockfile), "%s.lock", outfile);
snprintf(partfile, sizeof(partfile), "%s.part", outfile);
lockfd = aquire_lock(lockfile);
if (access(outfile, F_OK) == 0)
goto fetch_done;
/* enable insecure mode when http. This may be useful when it redirects to https */
if (insecure || strstr(url, "http://") == url) {
add_opt(&curlcmd, "--insecure");
add_opt(&wgetcmd, "--no-check-certificate");
}
if (access(partfile, F_OK) == 0) {
printf("Partial download found. Trying to resume.\n");
add_opt(&curlcmd, "--continue-at");
add_opt(&curlcmd, "-");
add_opt(&wgetcmd, "-c");
}
add_opt(&curlcmd, url);
add_opt(&wgetcmd, url);
status = fork_exec(curlcmd.argv, 0);
/* CURLE_RANGE_ERROR (33)
The server does not support or accept range requests. */
if (status == 33) {
unlink(partfile);
if( curlcmd.argc >=3) {
/* remove --continue-at - options */
curlcmd.argv[curlcmd.argc-3] = curlcmd.argv[curlcmd.argc-1];
curlcmd.argv[curlcmd.argc-2] = NULL;
curlcmd.argc -= 2;
status = fork_exec(curlcmd.argv, 0);
}
}
/* is we failed execute curl, then fallback to wget */
if (status == 201)
status = fork_exec(wgetcmd.argv, 1);
/* only rename completed downloads */
if (status == 0)
rename(partfile, outfile);
fetch_done:
release_lock(lockfd);
// give other processes the chance to aquire the lock if they have the file open
sleep(0);
if (status == 0 || try_lock(lockfd))
unlink(lockfile);
close(lockfd);
return status;
}
void sighandler(int sig)
{
switch(sig) {
case SIGABRT:
case SIGINT:
case SIGQUIT:
case SIGTERM:
unlink(lockfile);
exit(0);
break;
default:
break;
}
}
/* exit codes get passed through from curl/wget (so we can check in abuild
whether the server does not support resuming). Additional exit codes:
200: fork failed
201: curl/wget could not be started
202: curl/wget did not terminate normally
203: usage displayed */
int main(int argc, char *argv[])
{
int opt;
bool insecure = false;
char *destdir = "/var/cache/distfiles";
program = argv[0];
while ((opt = getopt(argc, argv, "hd:k")) != -1) {
switch (opt) {
case 'h':
return usage(0);
break;
case 'd':
destdir = optarg;
break;
case 'k':
insecure = true;
break;
default:
printf("Unknown option '%c'\n", opt);
return usage(1);
break;
}
}
argv += optind;
argc -= optind;
if (argc != 1)
return usage(203);
signal(SIGABRT, sighandler);
signal(SIGINT, sighandler);
signal(SIGQUIT, sighandler);
signal(SIGTERM, sighandler);
return fetch(argv[0], destdir, insecure);
}