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qemu-e2k/tools/virtiofsd/helper.c
Miklos Szeredi 5fe319a7b1 virtiofsd: passthrough_ll: add fallback for racy ops 
We have two operations that cannot be done race-free on a symlink in
certain cases: utimes and link.

Add racy fallback for these if the race-free method doesn't work.  We do
our best to avoid races even in this case:

  - get absolute path by reading /proc/self/fd/NN symlink

  - lookup parent directory: after this we are safe against renames in
    ancestors

  - lookup name in parent directory, and verify that we got to the original
    inode,  if not retry the whole thing

Both utimes(2) and link(2) hold i_lock on the inode across the operation,
so a racing rename/delete by this fuse instance is not possible, only from
other entities changing the filesystem.

If the "norace" option is given, then disable the racy fallbacks.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
2020-01-23 16:41:36 +00:00

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/*
* FUSE: Filesystem in Userspace
* Copyright (C) 2001-2007 Miklos Szeredi <miklos@szeredi.hu>
*
* Helper functions to create (simple) standalone programs. With the
* aid of these functions it should be possible to create full FUSE
* file system by implementing nothing but the request handlers.
* This program can be distributed under the terms of the GNU LGPLv2.
* See the file COPYING.LIB.
*/
#include "qemu/osdep.h"
#include "fuse_i.h"
#include "fuse_lowlevel.h"
#include "fuse_misc.h"
#include "fuse_opt.h"
#include <errno.h>
#include <limits.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <unistd.h>
#define FUSE_HELPER_OPT(t, p) \
{ \
t, offsetof(struct fuse_cmdline_opts, p), 1 \
}
#define FUSE_HELPER_OPT_VALUE(t, p, v) \
{ \
t, offsetof(struct fuse_cmdline_opts, p), v \
}
static const struct fuse_opt fuse_helper_opts[] = {
FUSE_HELPER_OPT("-h", show_help),
FUSE_HELPER_OPT("--help", show_help),
FUSE_HELPER_OPT("-V", show_version),
FUSE_HELPER_OPT("--version", show_version),
FUSE_HELPER_OPT("--print-capabilities", print_capabilities),
FUSE_HELPER_OPT("-d", debug),
FUSE_HELPER_OPT("debug", debug),
FUSE_HELPER_OPT("-d", foreground),
FUSE_HELPER_OPT("debug", foreground),
FUSE_OPT_KEY("-d", FUSE_OPT_KEY_KEEP),
FUSE_OPT_KEY("debug", FUSE_OPT_KEY_KEEP),
FUSE_HELPER_OPT("-f", foreground),
FUSE_HELPER_OPT_VALUE("--daemonize", foreground, 0),
FUSE_HELPER_OPT("fsname=", nodefault_subtype),
FUSE_OPT_KEY("fsname=", FUSE_OPT_KEY_KEEP),
FUSE_HELPER_OPT("subtype=", nodefault_subtype),
FUSE_OPT_KEY("subtype=", FUSE_OPT_KEY_KEEP),
FUSE_HELPER_OPT("max_idle_threads=%u", max_idle_threads),
FUSE_OPT_END
};
struct fuse_conn_info_opts {
int atomic_o_trunc;
int no_remote_posix_lock;
int no_remote_flock;
int splice_write;
int splice_move;
int splice_read;
int no_splice_write;
int no_splice_move;
int no_splice_read;
int auto_inval_data;
int no_auto_inval_data;
int no_readdirplus;
int no_readdirplus_auto;
int async_dio;
int no_async_dio;
int writeback_cache;
int no_writeback_cache;
int async_read;
int sync_read;
unsigned max_write;
unsigned max_readahead;
unsigned max_background;
unsigned congestion_threshold;
unsigned time_gran;
int set_max_write;
int set_max_readahead;
int set_max_background;
int set_congestion_threshold;
int set_time_gran;
};
#define CONN_OPTION(t, p, v) \
{ \
t, offsetof(struct fuse_conn_info_opts, p), v \
}
static const struct fuse_opt conn_info_opt_spec[] = {
CONN_OPTION("max_write=%u", max_write, 0),
CONN_OPTION("max_write=", set_max_write, 1),
CONN_OPTION("max_readahead=%u", max_readahead, 0),
CONN_OPTION("max_readahead=", set_max_readahead, 1),
CONN_OPTION("max_background=%u", max_background, 0),
CONN_OPTION("max_background=", set_max_background, 1),
CONN_OPTION("congestion_threshold=%u", congestion_threshold, 0),
CONN_OPTION("congestion_threshold=", set_congestion_threshold, 1),
CONN_OPTION("sync_read", sync_read, 1),
CONN_OPTION("async_read", async_read, 1),
CONN_OPTION("atomic_o_trunc", atomic_o_trunc, 1),
CONN_OPTION("no_remote_lock", no_remote_posix_lock, 1),
CONN_OPTION("no_remote_lock", no_remote_flock, 1),
CONN_OPTION("no_remote_flock", no_remote_flock, 1),
CONN_OPTION("no_remote_posix_lock", no_remote_posix_lock, 1),
CONN_OPTION("splice_write", splice_write, 1),
CONN_OPTION("no_splice_write", no_splice_write, 1),
CONN_OPTION("splice_move", splice_move, 1),
CONN_OPTION("no_splice_move", no_splice_move, 1),
CONN_OPTION("splice_read", splice_read, 1),
CONN_OPTION("no_splice_read", no_splice_read, 1),
CONN_OPTION("auto_inval_data", auto_inval_data, 1),
CONN_OPTION("no_auto_inval_data", no_auto_inval_data, 1),
CONN_OPTION("readdirplus=no", no_readdirplus, 1),
CONN_OPTION("readdirplus=yes", no_readdirplus, 0),
CONN_OPTION("readdirplus=yes", no_readdirplus_auto, 1),
CONN_OPTION("readdirplus=auto", no_readdirplus, 0),
CONN_OPTION("readdirplus=auto", no_readdirplus_auto, 0),
CONN_OPTION("async_dio", async_dio, 1),
CONN_OPTION("no_async_dio", no_async_dio, 1),
CONN_OPTION("writeback_cache", writeback_cache, 1),
CONN_OPTION("no_writeback_cache", no_writeback_cache, 1),
CONN_OPTION("time_gran=%u", time_gran, 0),
CONN_OPTION("time_gran=", set_time_gran, 1),
FUSE_OPT_END
};
void fuse_cmdline_help(void)
{
printf(" -h --help print help\n"
" -V --version print version\n"
" --print-capabilities print vhost-user.json\n"
" -d -o debug enable debug output (implies -f)\n"
" -f foreground operation\n"
" --daemonize run in background\n"
" -o max_idle_threads the maximum number of idle worker "
"threads\n"
" allowed (default: 10)\n"
" -o norace disable racy fallback\n"
" default: false\n"
);
}
static int fuse_helper_opt_proc(void *data, const char *arg, int key,
struct fuse_args *outargs)
{
(void)data;
(void)outargs;
switch (key) {
case FUSE_OPT_KEY_NONOPT:
fuse_log(FUSE_LOG_ERR, "fuse: invalid argument `%s'\n", arg);
return -1;
default:
/* Pass through unknown options */
return 1;
}
}
int fuse_parse_cmdline(struct fuse_args *args, struct fuse_cmdline_opts *opts)
{
memset(opts, 0, sizeof(struct fuse_cmdline_opts));
opts->max_idle_threads = 10;
opts->foreground = 1;
if (fuse_opt_parse(args, opts, fuse_helper_opts, fuse_helper_opt_proc) ==
-1) {
return -1;
}
return 0;
}
int fuse_daemonize(int foreground)
{
int ret = 0, rett;
if (!foreground) {
int nullfd;
int waiter[2];
char completed;
if (pipe(waiter)) {
perror("fuse_daemonize: pipe");
return -1;
}
/*
* demonize current process by forking it and killing the
* parent. This makes current process as a child of 'init'.
*/
switch (fork()) {
case -1:
perror("fuse_daemonize: fork");
return -1;
case 0:
break;
default:
_exit(read(waiter[0], &completed,
sizeof(completed) != sizeof(completed)));
}
if (setsid() == -1) {
perror("fuse_daemonize: setsid");
return -1;
}
ret = chdir("/");
nullfd = open("/dev/null", O_RDWR, 0);
if (nullfd != -1) {
rett = dup2(nullfd, 0);
if (!ret) {
ret = rett;
}
rett = dup2(nullfd, 1);
if (!ret) {
ret = rett;
}
rett = dup2(nullfd, 2);
if (!ret) {
ret = rett;
}
if (nullfd > 2) {
close(nullfd);
}
}
/* Propagate completion of daemon initialization */
completed = 1;
rett = write(waiter[1], &completed, sizeof(completed));
if (!ret) {
ret = rett;
}
close(waiter[0]);
close(waiter[1]);
} else {
ret = chdir("/");
}
return ret;
}
void fuse_apply_conn_info_opts(struct fuse_conn_info_opts *opts,
struct fuse_conn_info *conn)
{
if (opts->set_max_write) {
conn->max_write = opts->max_write;
}
if (opts->set_max_background) {
conn->max_background = opts->max_background;
}
if (opts->set_congestion_threshold) {
conn->congestion_threshold = opts->congestion_threshold;
}
if (opts->set_time_gran) {
conn->time_gran = opts->time_gran;
}
if (opts->set_max_readahead) {
conn->max_readahead = opts->max_readahead;
}
#define LL_ENABLE(cond, cap) \
if (cond) \
conn->want |= (cap)
#define LL_DISABLE(cond, cap) \
if (cond) \
conn->want &= ~(cap)
LL_ENABLE(opts->splice_read, FUSE_CAP_SPLICE_READ);
LL_DISABLE(opts->no_splice_read, FUSE_CAP_SPLICE_READ);
LL_ENABLE(opts->splice_write, FUSE_CAP_SPLICE_WRITE);
LL_DISABLE(opts->no_splice_write, FUSE_CAP_SPLICE_WRITE);
LL_ENABLE(opts->splice_move, FUSE_CAP_SPLICE_MOVE);
LL_DISABLE(opts->no_splice_move, FUSE_CAP_SPLICE_MOVE);
LL_ENABLE(opts->auto_inval_data, FUSE_CAP_AUTO_INVAL_DATA);
LL_DISABLE(opts->no_auto_inval_data, FUSE_CAP_AUTO_INVAL_DATA);
LL_DISABLE(opts->no_readdirplus, FUSE_CAP_READDIRPLUS);
LL_DISABLE(opts->no_readdirplus_auto, FUSE_CAP_READDIRPLUS_AUTO);
LL_ENABLE(opts->async_dio, FUSE_CAP_ASYNC_DIO);
LL_DISABLE(opts->no_async_dio, FUSE_CAP_ASYNC_DIO);
LL_ENABLE(opts->writeback_cache, FUSE_CAP_WRITEBACK_CACHE);
LL_DISABLE(opts->no_writeback_cache, FUSE_CAP_WRITEBACK_CACHE);
LL_ENABLE(opts->async_read, FUSE_CAP_ASYNC_READ);
LL_DISABLE(opts->sync_read, FUSE_CAP_ASYNC_READ);
LL_DISABLE(opts->no_remote_posix_lock, FUSE_CAP_POSIX_LOCKS);
LL_DISABLE(opts->no_remote_flock, FUSE_CAP_FLOCK_LOCKS);
}
struct fuse_conn_info_opts *fuse_parse_conn_info_opts(struct fuse_args *args)
{
struct fuse_conn_info_opts *opts;
opts = calloc(1, sizeof(struct fuse_conn_info_opts));
if (opts == NULL) {
fuse_log(FUSE_LOG_ERR, "calloc failed\n");
return NULL;
}
if (fuse_opt_parse(args, opts, conn_info_opt_spec, NULL) == -1) {
free(opts);
return NULL;
}
return opts;
}
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