[PATCH 03/10] libxfs: add xfile support

Darrick J. Wong
2023-12-31T22:15:20Z

Port the xfile functionality (anonymous pageable file-index memory) from
the kernel. In userspace, we try to use memfd() to create tmpfs files
that are not in any namespace, matching the kernel.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
configure.ac | 4 +
include/builddefs.in | 4 +
libxfs/Makefile | 15 +++
libxfs/xfile.c | 265 +++++++++++++++++++++++++++++++++++++++++++++++++
libxfs/xfile.h | 56 ++++++++++
m4/package_libcdev.m4 | 66 ++++++++++++
repair/xfs_repair.c | 15 +++
7 files changed, 425 insertions(+)
create mode 100644 libxfs/xfile.c
create mode 100644 libxfs/xfile.h

diff --git a/configure.ac b/configure.ac
index 2034f02e59e..38b62619a7a 100644
--- a/configure.ac
+++ b/configure.ac
@@ -253,6 +253,10 @@ AC_CHECK_SIZEOF([char *])
AC_TYPE_UMODE_T
AC_MANUAL_FORMAT
AC_HAVE_LIBURCU_ATOMIC64
+AC_HAVE_MEMFD_CLOEXEC
+AC_HAVE_MEMFD_NOEXEC_SEAL
+AC_HAVE_O_TMPFILE
+AC_HAVE_MKOSTEMP_CLOEXEC

AC_CONFIG_FILES([include/builddefs])
AC_OUTPUT
diff --git a/include/builddefs.in b/include/builddefs.in
index 43025ba4fcc..eb7f6ba4f03 100644
--- a/include/builddefs.in
+++ b/include/builddefs.in
@@ -130,6 +130,10 @@ CROND_DIR = @crond_dir@
HAVE_UDEV = @have_udev@
UDEV_RULE_DIR = @udev_rule_dir@
HAVE_LIBURCU_ATOMIC64 = @have_liburcu_atomic64@
+HAVE_MEMFD_CLOEXEC = @have_memfd_cloexec@
+HAVE_MEMFD_NOEXEC_SEAL = @have_memfd_noexec_seal@
+HAVE_O_TMPFILE = @have_o_tmpfile@
+HAVE_MKOSTEMP_CLOEXEC = @have_mkostemp_cloexec@

GCCFLAGS = -funsigned-char -fno-strict-aliasing -Wall
# -Wbitwise -Wno-transparent-union -Wno-old-initializer -Wno-decl
diff --git a/libxfs/Makefile b/libxfs/Makefile
index 6f688c0ad25..68b366072da 100644
--- a/libxfs/Makefile
+++ b/libxfs/Makefile
@@ -26,6 +26,7 @@ HFILES = \
libxfs_priv.h \
linux-err.h \
topology.h \
+ xfile.h \
xfs_ag_resv.h \
xfs_alloc.h \
xfs_alloc_btree.h \
@@ -66,6 +67,7 @@ CFILES = cache.c \
topology.c \
trans.c \
util.c \
+ xfile.c \
xfs_ag.c \
xfs_ag_resv.c \
xfs_alloc.c \
@@ -112,6 +114,19 @@ CFILES = cache.c \
#
#LCFLAGS +=

+ifeq ($(HAVE_MEMFD_CLOEXEC),yes)
+ LCFLAGS += -DHAVE_MEMFD_CLOEXEC
+endif
+ifeq ($(HAVE_MEMFD_NOEXEC_SEAL),yes)
+ LCFLAGS += -DHAVE_MEMFD_NOEXEC_SEAL
+endif
+ifeq ($(HAVE_O_TMPFILE),yes)
+ LCFLAGS += -DHAVE_O_TMPFILE
+endif
+ifeq ($(HAVE_MKOSTEMP_CLOEXEC),yes)
+ LCFLAGS += -DHAVE_MKOSTEMP_CLOEXEC
+endif
+
FCFLAGS = -I.

LTLIBS = $(LIBPTHREAD) $(LIBRT)
diff --git a/libxfs/xfile.c b/libxfs/xfile.c
new file mode 100644
index 00000000000..57694d33498
--- /dev/null
+++ b/libxfs/xfile.c
@@ -0,0 +1,265 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2021-2024 Oracle. All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#include "libxfs_priv.h"
+#include "libxfs.h"
+#include "libxfs/xfile.h"
+#ifdef HAVE_MEMFD_NOEXEC_SEAL
+# include <linux/memfd.h>
+#endif
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+/*
+ * Swappable Temporary Memory
+ * ==========================
+ *
+ * Offline checking sometimes needs to be able to stage a large amount of data
+ * in memory. This information might not fit in the available memory and it
+ * doesn't all need to be accessible at all times. In other words, we want an
+ * indexed data buffer to store data that can be paged out.
+ *
+ * memfd files meet those requirements. Therefore, the xfile mechanism uses
+ * one to store our staging data. The xfile must be freed with xfile_destroy.
+ *
+ * xfiles assume that the caller will handle all required concurrency
+ * management; file locks are not taken.
+ */
+
+/*
+ * Open a memory-backed fd to back an xfile. We require close-on-exec here,
+ * because these memfd files function as windowed RAM and hence should never
+ * be shared with other processes.
+ */
+static int
+xfile_create_fd(
+ const char *description)
+{
+ int fd = -1;
+ int ret;
+
+#ifdef HAVE_MEMFD_CLOEXEC
+
+# ifdef HAVE_MEMFD_NOEXEC_SEAL
+ /*
+ * Starting with Linux 6.3, there's a new MFD_NOEXEC_SEAL flag that
+ * disables the longstanding memfd behavior that files are created with
+ * the executable bit set, and seals the file against it being turned
+ * back on. Using this bit on older kernels produces EINVAL, so we
+ * try this twice.
+ */
+ fd = memfd_create(description, MFD_CLOEXEC | MFD_NOEXEC_SEAL);
+ if (fd >= 0)
+ goto got_fd;
+# endif /* HAVE_MEMFD_NOEXEC_SEAL */
+
+ /* memfd_create exists in kernel 3.17 (2014) and glibc 2.27 (2018). */
+ fd = memfd_create(description, MFD_CLOEXEC);
+ if (fd >= 0)
+ goto got_fd;
+#endif /* HAVE_MEMFD_CLOEXEC */
+
+#ifdef HAVE_O_TMPFILE
+ /*
+ * O_TMPFILE exists as of kernel 3.11 (2013), which means that if we
+ * find it, we're pretty safe in assuming O_CLOEXEC exists too.
+ */
+ fd = open("/dev/shm", O_TMPFILE | O_CLOEXEC | O_RDWR, 0600);
+ if (fd >= 0)
+ goto got_fd;
+
+ fd = open("/tmp", O_TMPFILE | O_CLOEXEC | O_RDWR, 0600);
+ if (fd >= 0)
+ goto got_fd;
+#endif
+
+#ifdef HAVE_MKOSTEMP_CLOEXEC
+ /*
+ * mkostemp exists as of glibc 2.7 (2007) and O_CLOEXEC exists as of
+ * kernel 2.6.23 (2007).
+ */
+ fd = mkostemp("libxfsXXXXXX", O_CLOEXEC);
+ if (fd >= 0)
+ goto got_fd;
+#endif
+
+#if !defined(HAVE_MEMFD_CLOEXEC) && \
+ !defined(HAVE_O_TMPFILE) && \
+ !defined(HAVE_MKOSTEMP_CLOEXEC)
+# error System needs memfd_create, O_TMPFILE, or O_CLOEXEC to build!
+#endif
+
+ if (!errno)
+ errno = EOPNOTSUPP;
+ return -1;
+got_fd:
+ /*
+ * Turn off mode bits we don't want -- group members and others should
+ * not have access to the xfile, nor it be executable. memfds are
+ * created with mode 0777, but we'll be careful just in case the other
+ * implementations fail to set 0600.
+ */
+ ret = fchmod(fd, 0600);
+ if (ret)
+ perror("disabling xfile executable bit");
+
+ return fd;
+}
+
+/*
+ * Create an xfile of the given size. The description will be used in the
+ * trace output.
+ */
+int
+xfile_create(
+ const char *description,
+ struct xfile **xfilep)
+{
+ struct xfile *xf;
+ int error;
+
+ xf = kmem_alloc(sizeof(struct xfile), KM_MAYFAIL);
+ if (!xf)
+ return -ENOMEM;
+
+ xf->fd = xfile_create_fd(description);
+ if (xf->fd < 0) {
+ error = -errno;
+ kmem_free(xf);
+ return error;
+ }
+
+ *xfilep = xf;
+ return 0;
+}
+
+/* Close the file and release all resources. */
+void
+xfile_destroy(
+ struct xfile *xf)
+{
+ close(xf->fd);
+ kmem_free(xf);
+}
+
+static inline loff_t
+xfile_maxbytes(
+ struct xfile *xf)
+{
+ if (sizeof(loff_t) == 8)
+ return LLONG_MAX;
+ return LONG_MAX;
+}
+
+/*
+ * Read a memory object directly from the xfile's page cache. Unlike regular
+ * pread, we return -E2BIG and -EFBIG for reads that are too large or at too
+ * high an offset, instead of truncating the read. Otherwise, we return
+ * bytes read or an error code, like regular pread.
+ */
+ssize_t
+xfile_pread(
+ struct xfile *xf,
+ void *buf,
+ size_t count,
+ loff_t pos)
+{
+ ssize_t ret;
+
+ if (count > INT_MAX)
+ return -E2BIG;
+ if (xfile_maxbytes(xf) - pos < count)
+ return -EFBIG;
+
+ ret = pread(xf->fd, buf, count, pos);
+ if (ret >= 0)
+ return ret;
+ return -errno;
+}
+
+/*
+ * Write a memory object directly to the xfile's page cache. Unlike regular
+ * pwrite, we return -E2BIG and -EFBIG for writes that are too large or at too
+ * high an offset, instead of truncating the write. Otherwise, we return
+ * bytes written or an error code, like regular pwrite.
+ */
+ssize_t
+xfile_pwrite(
+ struct xfile *xf,
+ const void *buf,
+ size_t count,
+ loff_t pos)
+{
+ ssize_t ret;
+
+ if (count > INT_MAX)
+ return -E2BIG;
+ if (xfile_maxbytes(xf) - pos < count)
+ return -EFBIG;
+
+ ret = pwrite(xf->fd, buf, count, pos);
+ if (ret >= 0)
+ return ret;
+ return -errno;
+}
+
+/* Compute the number of bytes used by a xfile. */
+unsigned long long
+xfile_bytes(
+ struct xfile *xf)
+{
+ struct xfile_stat xs;
+ int ret;
+
+ ret = xfile_stat(xf, &xs);
+ if (ret)
+ return 0;
+
+ return xs.bytes;
+}
+
+/* Query stat information for an xfile. */
+int
+xfile_stat(
+ struct xfile *xf,
+ struct xfile_stat *statbuf)
+{
+ struct stat ks;
+ int error;
+
+ error = fstat(xf->fd, &ks);
+ if (error)
+ return -errno;
+
+ statbuf->size = ks.st_size;
+ statbuf->bytes = (unsigned long long)ks.st_blocks << 9;
+ return 0;
+}
+
+/* Dump an xfile to stdout. */
+int
+xfile_dump(
+ struct xfile *xf)
+{
+ char *argv[] = {"od", "-tx1", "-Ad", "-c", NULL};
+ pid_t child;
+ int i;
+
+ child = fork();
+ if (child != 0) {
+ int wstatus;
+
+ wait(&wstatus);
+ return wstatus == 0 ? 0 : -EIO;
+ }
+
+ /* reroute our xfile to stdin and shut everything else */
+ dup2(xf->fd, 0);
+ for (i = 3; i < 1024; i++)
+ close(i);
+
+ return execvp("od", argv);
+}
diff --git a/libxfs/xfile.h b/libxfs/xfile.h
new file mode 100644
index 00000000000..4218c17e8bf
--- /dev/null
+++ b/libxfs/xfile.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (c) 2021-2024 Oracle. All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#ifndef __LIBXFS_XFILE_H__
+#define __LIBXFS_XFILE_H__
+
+struct xfile {
+ int fd;
+};
+
+int xfile_create(const char *description, struct xfile **xfilep);
+void xfile_destroy(struct xfile *xf);
+
+ssize_t xfile_pread(struct xfile *xf, void *buf, size_t count, loff_t pos);
+ssize_t xfile_pwrite(struct xfile *xf, const void *buf, size_t count, loff_t pos);
+
+/*
+ * Load an object. Since we're treating this file as "memory", any error or
+ * short IO is treated as a failure to allocate memory.
+ */
+static inline int
+xfile_obj_load(struct xfile *xf, void *buf, size_t count, loff_t pos)
+{
+ ssize_t ret = xfile_pread(xf, buf, count, pos);
+
+ if (ret < 0 || ret != count)
+ return -ENOMEM;
+ return 0;
+}
+
+/*
+ * Store an object. Since we're treating this file as "memory", any error or
+ * short IO is treated as a failure to allocate memory.
+ */
+static inline int
+xfile_obj_store(struct xfile *xf, const void *buf, size_t count, loff_t pos)
+{
+ ssize_t ret = xfile_pwrite(xf, buf, count, pos);
+
+ if (ret < 0 || ret != count)
+ return -ENOMEM;
+ return 0;
+}
+
+struct xfile_stat {
+ loff_t size;
+ unsigned long long bytes;
+};
+
+int xfile_stat(struct xfile *xf, struct xfile_stat *statbuf);
+unsigned long long xfile_bytes(struct xfile *xf);
+int xfile_dump(struct xfile *xf);
+
+#endif /* __LIBXFS_XFILE_H__ */
diff --git a/m4/package_libcdev.m4 b/m4/package_libcdev.m4
index 174070651ec..c81a7a031d2 100644
--- a/m4/package_libcdev.m4
+++ b/m4/package_libcdev.m4
@@ -531,3 +531,69 @@ AC_DEFUN([AC_PACKAGE_CHECK_LTO],
AC_SUBST(lto_cflags)
AC_SUBST(lto_ldflags)
])
+
+#
+# Check if we have a memfd_create syscall with a MFD_CLOEXEC flag
+#
+AC_DEFUN([AC_HAVE_MEMFD_CLOEXEC],
+ [ AC_MSG_CHECKING([for memfd_fd and MFD_CLOEXEC])
+ AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#define _GNU_SOURCE
+#include <sys/mman.h>
+ ]], [[
+ return memfd_create("xfs", MFD_CLOEXEC);
+ ]])],[have_memfd_cloexec=yes
+ AC_MSG_RESULT(yes)],[AC_MSG_RESULT(no)])
+ AC_SUBST(have_memfd_cloexec)
+ ])
+
+#
+# Check if we have a memfd_create syscall with a MFD_NOEXEC_SEAL flag
+#
+AC_DEFUN([AC_HAVE_MEMFD_NOEXEC_SEAL],
+ [ AC_MSG_CHECKING([for memfd_fd and MFD_NOEXEC_SEAL])
+ AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#define _GNU_SOURCE
+#include <linux/memfd.h>
+#include <sys/mman.h>
+ ]], [[
+ return memfd_create("xfs", MFD_NOEXEC_SEAL);
+ ]])],[have_memfd_noexec_seal=yes
+ AC_MSG_RESULT(yes)],[AC_MSG_RESULT(no)])
+ AC_SUBST(have_memfd_noexec_seal)
+ ])
+
+#
+# Check if we have the O_TMPFILE flag
+#
+AC_DEFUN([AC_HAVE_O_TMPFILE],
+ [ AC_MSG_CHECKING([for O_TMPFILE])
+ AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+ ]], [[
+ return open("nowhere", O_TMPFILE, 0600);
+ ]])],[have_o_tmpfile=yes
+ AC_MSG_RESULT(yes)],[AC_MSG_RESULT(no)])
+ AC_SUBST(have_o_tmpfile)
+ ])
+
+#
+# Check if we have mkostemp with the O_CLOEXEC flag
+#
+AC_DEFUN([AC_HAVE_MKOSTEMP_CLOEXEC],
+ [ AC_MSG_CHECKING([for mkostemp and O_CLOEXEC])
+ AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+#define _GNU_SOURCE
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdlib.h>
+ ]], [[
+ return mkostemp("nowhere", O_TMPFILE);
+ ]])],[have_mkostemp_cloexec=yes
+ AC_MSG_RESULT(yes)],[AC_MSG_RESULT(no)])
+ AC_SUBST(have_mkostemp_cloexec)
+ ])
diff --git a/repair/xfs_repair.c b/repair/xfs_repair.c
index d4f99f36f71..01f92e841f2 100644
--- a/repair/xfs_repair.c
+++ b/repair/xfs_repair.c
@@ -953,6 +953,20 @@ phase_end(
platform_crash();
}

+/* Try to allow as many memfds as possible. */
+static void
+bump_max_fds(void)
+{
+ struct rlimit rlim = { };
+ int ret;
+
+ ret = getrlimit(RLIMIT_NOFILE, &rlim);
+ if (!ret) {
+ rlim.rlim_cur = rlim.rlim_max;
+ setrlimit(RLIMIT_NOFILE, &rlim);
+ }
+}
+
int
main(int argc, char **argv)
{
@@ -972,6 +986,7 @@ main(int argc, char **argv)
bindtextdomain(PACKAGE, LOCALEDIR);
textdomain(PACKAGE);
dinode_bmbt_translation_init();
+ bump_max_fds();

temp_mp = &xfs_m;
setbuf(stdout, NULL);