[DTrace-devel] [PATCH 3/3] daemon: support libfuse 2
Nick Alcock
nick.alcock at oracle.com
Mon Nov 7 22:19:30 UTC 2022
So it turns out that some people want to use libfuse 2 still, even
though it's been obsoleted by libfuse 3 for nearly a decade. This turns
out to be not terribly difficult!
There are two major changess that impact us (ignoring the options-
parsing thing fixed in the last commit):
- libfuse 2 has a 'channel' abstraction in which the fd to the kernel
is nested. libfuse 3 dropped it because it turned out there was only
ever one of them so the abstraction was redundant, but that makes it
easy for us to pick the fd out: we can grab the fuse_session_next_chan()
without ever worrying that we might have to call that function more
than once or deal with more than one channel.
This changes the main read loop() enough that we can just implement
it twice.
- that's good because of another annoying difference: OL carries a
NUMA-aware API which actually changes the public API of libfuse's
fuse_session_receive_buf function (I guess the assumption was that
nobody else would implement their own event loop, which is... a
heroic assumption given that a quick search shows a bunch of users
including minor ones like QEMU). This is hard to check for because
the extra functions you need to call to actually turn this behaviour
on were never added to the symbol version file, so you can't link
with them. So we detect these functions using the macros just added
to do straight compilation checking, with no linking, and use their
presence as a clue that fuse_session_receive_buf has the NUMA-aware
API change. (We don't use the NUMA stuff: it's only useful if you're
using a multithreaded event loop, which we're not.)
We currently handle systems with both libfuse 2 and 3 by checking that
libfuse 3 is available, and if not, falling back to libfuse 2 (and if
that isn't present either you get a link failure). Thus libfuse 3 is
preferred if both are present.
Signed-off-by: Nick Alcock <nick.alcock at oracle.com>
---
Makeconfig | 2 ++
dtprobed/Build | 11 +++++--
dtprobed/dtprobed.c | 78 ++++++++++++++++++++++++++++++++++++++++++++-
dtrace.spec | 11 +++++--
4 files changed, 97 insertions(+), 5 deletions(-)
diff --git a/Makeconfig b/Makeconfig
index 15614384fd94..52071e29935b 100644
--- a/Makeconfig
+++ b/Makeconfig
@@ -97,4 +97,6 @@ $(eval $(call check-symbol-rule,STRRSTR,strrstr,c))
$(eval $(call check-symbol-rule,WAITFD,waitfd,c))
$(eval $(call check-symbol-rule,LIBSYSTEMD,sd_notify,systemd))
$(eval $(call check-symbol-rule,FUSE_LOG,fuse_set_log_func,fuse3))
+$(eval $(call check-symbol-rule,FUSE3,fuse_session_receive_buf,fuse3))
+$(eval $(call check-header-rule,FUSE_NUMA,fuse_set_numa,fuse/fuse_lowlevel))
$(eval $(call check-header-symbol-rule,CLOSE_RANGE,close_range(3,~0U,0),c,unistd))
diff --git a/dtprobed/Build b/dtprobed/Build
index 6775267ec77f..6041cd9fc0f3 100644
--- a/dtprobed/Build
+++ b/dtprobed/Build
@@ -5,11 +5,18 @@
CMDS += dtprobed
+# Support FUSE 2 as well as FUSE 3.
+ifdef HAVE_FUSE3
+LIBFUSE := fuse3
+else
+LIBFUSE := fuse
+endif
+
dtprobed_DIR := $(current-dir)
dtprobed_TARGET = dtprobed
dtprobed_CPPFLAGS := -I. -Idtprobed -Ilibproc -Ilibcommon -Ilibport
-dtprobed_CFLAGS := $(shell pkg-config --cflags fuse3)
-dtprobed_LIBS := -lcommon -lproc -lcommon -lport -lelf $(shell pkg-config --libs fuse3)
+dtprobed_CFLAGS := $(shell pkg-config --cflags $(LIBFUSE))
+dtprobed_LIBS := -lcommon -lproc -lcommon -lport -lelf $(shell pkg-config --libs $(LIBFUSE))
dtprobed_DEPS := libproc.a libcommon.a libport.a
dtprobed_SOURCES := dtprobed.c
dtprobed_LIBSOURCES := libproc libcommon
diff --git a/dtprobed/dtprobed.c b/dtprobed/dtprobed.c
index b76bc213e650..77d66772209c 100644
--- a/dtprobed/dtprobed.c
+++ b/dtprobed/dtprobed.c
@@ -93,6 +93,31 @@ dt_debug_printf(const char *subsys, const char *fmt, va_list ap)
}
}
+#if HAVE_FUSE3
+static void
+old_fuse_init(struct fuse_session *cuse_session) {}
+
+static int
+session_fd(struct fuse_session *cuse_session)
+{
+ return fuse_session_fd(cuse_session);
+}
+#else /* FUSE 2 */
+static struct fuse_chan *cuse_chan;
+
+static void
+old_fuse_init(struct fuse_session *cuse_session)
+{
+ cuse_chan = fuse_session_next_chan(cuse_session, NULL);
+}
+
+static int
+session_fd(struct fuse_session *cuse_session)
+{
+ return fuse_chan_fd(cuse_chan);
+}
+#endif
+
/*
* States for the ioctl processing loop, which gets repeatedly called due to the
* request/reply nature of unrestricted FUSE ioctls.
@@ -141,6 +166,8 @@ setup_helper_device(int argc, char **argv, char *devname, dtprobed_userdata_t *u
return NULL;
}
+ old_fuse_init(cs);
+
if (multithreaded) {
fprintf(stderr, "CUSE thinks dtprobed is multithreaded!\n");
fprintf(stderr, "This should never happen.\n");
@@ -202,7 +229,7 @@ dof_parser_start(int sync_fd)
* Sandboxed parser child. Close unwanted fds and nail into
* seccomp jail.
*/
- close(fuse_session_fd(cuse_session));
+ close(session_fd(cuse_session));
close(parser_in_pipe[1]);
close(parser_out_pipe[0]);
if (!foreground)
@@ -507,6 +534,7 @@ err:
return -1;
}
+#if HAVE_FUSE3
static int
loop(void)
{
@@ -538,6 +566,54 @@ loop(void)
fuse_session_reset(cuse_session);
return ret < 0 ? -1 : 0;
}
+#else /* FUSE 2 */
+static int
+loop(void)
+{
+ struct pollfd fds[1];
+ void *buf;
+ size_t bufsize;
+ int ret = 0;
+
+ bufsize = fuse_chan_bufsize(cuse_chan);
+ buf = malloc(bufsize);
+ if (!buf) {
+ fprintf(stderr, "Cannot allocate memory for FUSE buffer\n");
+ return -1;
+ }
+
+ fds[0].fd = fuse_chan_fd(cuse_chan);
+ fds[0].events = POLLIN;
+
+ while (!fuse_session_exited(cuse_session)) {
+ struct fuse_buf fbuf = { .mem = buf, .size = bufsize };
+ struct fuse_chan *tmpch = cuse_chan;
+
+ if ((ret = poll(fds, 1, -1)) < 0)
+ break;
+
+ if (fds[0].revents != 0) {
+ if ((ret = fuse_session_receive_buf(cuse_session,
+ &fbuf, &tmpch)) <= 0) {
+ if (ret == -EINTR)
+ continue;
+
+ break;
+ }
+
+#ifdef HAVE_FUSE_NUMA
+ fuse_session_process_buf(cuse_session, &fbuf, tmpch, 0);
+#else
+ fuse_session_process_buf(cuse_session, &fbuf, tmpch);
+#endif
+ }
+ }
+
+ free(buf);
+ fuse_session_reset(cuse_session);
+ return ret < 0 ? -1 : 0;
+}
+#endif
static void
usage(void)
diff --git a/dtrace.spec b/dtrace.spec
index 0d87591dddc6..62515acd2700 100644
--- a/dtrace.spec
+++ b/dtrace.spec
@@ -55,9 +55,16 @@ BuildRequires: rpm
Name: dtrace
License: Universal Permissive License (UPL), Version 1.0
Group: Development/Tools
-Requires: cpp elfutils-libelf zlib libpcap fuse3 >= 3.2.0
-BuildRequires: glibc-headers bison flex zlib-devel elfutils-libelf-devel fuse3-devel >= 3.2.0 systemd systemd-devel
+Requires: cpp elfutils-libelf zlib libpcap
+BuildRequires: glibc-headers bison flex zlib-devel elfutils-libelf-devel systemd systemd-devel
BuildRequires: glibc-static %{glibc32} wireshark libpcap-devel valgrind-devel
+%if "%{?dist}" == ".el7"
+Requires: fuse
+BuildRequires: fuse-devel
+%else
+Requires: fuse3 >= 3.2.0
+BuildRequires: fuse3-devel >= 3.2.0
+%endif
%{?systemd_requires}
BuildRequires: kernel%{variant}-devel = %{build_kernel}
%if "%{?dist}" == ".el8"
--
2.35.1
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