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109 lines
2.5 KiB
C
109 lines
2.5 KiB
C
// Copyright (c) Meta Platforms, Inc. and affiliates.
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// SPDX-License-Identifier: GPL-3.0-or-later
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/*
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* QEMU's 9pfs server passes through O_NOATIME from the client. If the server
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* process doesn't have permission to use O_NOATIME (e.g., because it's being
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* run without privileges and it doesn't own the file), then the open will fail.
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* Overlayfs uses O_NOATIME, so overlayfs on top of 9pfs doesn't work. We work
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* around this with this LD_PRELOAD hack to remove O_NOATIME from open() and
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* fcntl() calls.
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*
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* As of QEMU 5.1.0, the 9pfs server falls back to removing O_NOATIME, so this
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* isn't necessary on newer versions.
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*/
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#include <dlfcn.h>
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#include <fcntl.h>
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#include <stdarg.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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#define ORIG(name) ({ \
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static typeof(&name) orig; \
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\
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if (!orig) { \
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void *tmp; \
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\
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tmp = dlsym(RTLD_NEXT, #name); \
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if (!tmp) { \
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fprintf(stderr, "%s\n", dlerror()); \
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abort(); \
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} \
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orig = tmp; \
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} \
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orig; \
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})
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#ifndef __OPEN_NEEDS_MODE
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/* From glibc fnctl.h. */
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#ifdef __O_TMPFILE
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# define __OPEN_NEEDS_MODE(oflag) \
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(((oflag) & O_CREAT) != 0 || ((oflag) & __O_TMPFILE) == __O_TMPFILE)
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#else
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# define __OPEN_NEEDS_MODE(oflag) (((oflag) & O_CREAT) != 0)
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#endif
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#endif
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#define OPEN_MODE(flags) ({ \
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mode_t mode = 0; \
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\
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if (__OPEN_NEEDS_MODE(flags)) { \
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va_list ap; \
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\
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va_start(ap, flags); \
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mode = va_arg(ap, mode_t); \
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va_end(ap); \
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} \
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mode; \
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})
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int open(const char *pathname, int flags, ...)
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{
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flags &= ~O_NOATIME;
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return ORIG(open)(pathname, flags, OPEN_MODE(flags));
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}
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int open64(const char *pathname, int flags, ...)
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{
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flags &= ~O_NOATIME;
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return ORIG(open64)(pathname, flags, OPEN_MODE(flags));
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}
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int openat(int dirfd, const char *pathname, int flags, ...)
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{
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flags &= ~O_NOATIME;
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return ORIG(openat)(dirfd, pathname, flags, OPEN_MODE(flags));
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}
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int openat64(int dirfd, const char *pathname, int flags, ...)
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{
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flags &= ~O_NOATIME;
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return ORIG(openat64)(dirfd, pathname, flags, OPEN_MODE(flags));
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}
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#define FCNTL_ARG(cmd) ({ \
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va_list ap; \
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void *arg; \
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\
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va_start(ap, cmd); \
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arg = va_arg(ap, void *); \
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va_end(ap); \
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if (cmd == F_SETFL) \
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arg = (void *)((uintptr_t)arg & ~O_NOATIME); \
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arg; \
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})
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int fcntl(int fd, int cmd, ...)
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{
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return ORIG(fcntl)(fd, cmd, FCNTL_ARG(cmd));
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}
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int fcntl64(int fd, int cmd, ...)
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{
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return ORIG(fcntl64)(fd, cmd, FCNTL_ARG(cmd));
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}
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