[ Upstream commit 47311db8e8 ]
Users may have explicitly configured their tracefs permissions; we
shouldn't overwrite those just because a second mount appeared.
Only clobber if the options were provided at mount time.
Note: the previous behavior was especially surprising in the presence of
automounted /sys/kernel/debug/tracing/.
Existing behavior:
## Pre-existing status: tracefs is 0755.
# stat -c '%A' /sys/kernel/tracing/
drwxr-xr-x
## (Re)trigger the automount.
# umount /sys/kernel/debug/tracing
# stat -c '%A' /sys/kernel/debug/tracing/.
drwx------
## Unexpected: the automount changed mode for other mount instances.
# stat -c '%A' /sys/kernel/tracing/
drwx------
New behavior (after this change):
## Pre-existing status: tracefs is 0755.
# stat -c '%A' /sys/kernel/tracing/
drwxr-xr-x
## (Re)trigger the automount.
# umount /sys/kernel/debug/tracing
# stat -c '%A' /sys/kernel/debug/tracing/.
drwxr-xr-x
## Expected: the automount does not change other mount instances.
# stat -c '%A' /sys/kernel/tracing/
drwxr-xr-x
Link: https://lkml.kernel.org/r/20220826174353.2.Iab6e5ea57963d6deca5311b27fb7226790d44406@changeid
Cc: stable@vger.kernel.org
Fixes: 4282d60689 ("tracefs: Add new tracefs file system")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
commit 851e99ebee upstream.
Al Viro brought it to my attention that the dentries may not be filled
when the parse_options() is called, causing the call to set_gid() to
possibly crash. It should only be called if parse_options() succeeds
totally anyway.
He suggested the logical place to do the update is in apply_options().
Link: https://lore.kernel.org/all/20220225165219.737025658@goodmis.org/
Link: https://lkml.kernel.org/r/20220225153426.1c4cab6b@gandalf.local.home
Cc: stable@vger.kernel.org
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: 48b27b6b51 ("tracefs: Set all files to the same group ownership as the mount option")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit 48b27b6b51 upstream.
As people have been asking to allow non-root processes to have access to
the tracefs directory, it was considered best to only allow groups to have
access to the directory, where it is easier to just set the tracefs file
system to a specific group (as other would be too dangerous), and that way
the admins could pick which processes would have access to tracefs.
Unfortunately, this broke tooling on Android that expected the other bit
to be set. For some special cases, for non-root tools to trace the system,
tracefs would be mounted and change the permissions of the top level
directory which gave access to all running tasks permission to the
tracing directory. Even though this would be dangerous to do in a
production environment, for testing environments this can be useful.
Now with the new changes to not allow other (which is still the proper
thing to do), it breaks the testing tooling. Now more code needs to be
loaded on the system to change ownership of the tracing directory.
The real solution is to have tracefs honor the gid=xxx option when
mounting. That is,
(tracing group tracing has value 1003)
mount -t tracefs -o gid=1003 tracefs /sys/kernel/tracing
should have it that all files in the tracing directory should be of the
given group.
Copy the logic from d_walk() from dcache.c and simplify it for the mount
case of tracefs if gid is set. All the files in tracefs will be walked and
their group will be set to the value passed in.
Link: https://lkml.kernel.org/r/20211207171729.2a54e1b3@gandalf.local.home
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reported-by: Kalesh Singh <kaleshsingh@google.com>
Reported-by: Yabin Cui <yabinc@google.com>
Fixes: 49d67e4457 ("tracefs: Have tracefs directories not set OTH permission bits by default")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
commit ee7f366699 upstream.
If directories in tracefs have their ownership changed, then any new files
and directories that are created under those directories should inherit
the ownership of the director they are created in.
Link: https://lkml.kernel.org/r/20211208075720.4855d180@gandalf.local.home
Cc: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Yabin Cui <yabinc@google.com>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: stable@vger.kernel.org
Fixes: 4282d60689 ("tracefs: Add new tracefs file system")
Reported-by: Kalesh Singh <kaleshsingh@google.com>
Reported: https://lore.kernel.org/all/CAC_TJve8MMAv+H_NdLSJXZUSoxOEq2zB_pVaJ9p=7H6Bu3X76g@mail.gmail.com/
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[ Upstream commit 49d67e4457 ]
The tracefs file system is by default mounted such that only root user can
access it. But there are legitimate reasons to create a group and allow
those added to the group to have access to tracing. By changing the
permissions of the tracefs mount point to allow access, it will allow
group access to the tracefs directory.
There should not be any real reason to allow all access to the tracefs
directory as it contains sensitive information. Have the default
permission of directories being created not have any OTH (other) bits set,
such that an admin that wants to give permission to a group has to first
disable all OTH bits in the file system.
Link: https://lkml.kernel.org/r/20210818153038.664127804@goodmis.org
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Extend some inode methods with an additional user namespace argument. A
filesystem that is aware of idmapped mounts will receive the user
namespace the mount has been marked with. This can be used for
additional permission checking and also to enable filesystems to
translate between uids and gids if they need to. We have implemented all
relevant helpers in earlier patches.
As requested we simply extend the exisiting inode method instead of
introducing new ones. This is a little more code churn but it's mostly
mechanical and doesnt't leave us with additional inode methods.
Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
If on boot up, lockdown is activated for tracefs, don't even bother creating
the files. This can also prevent instances from being created if lockdown is
in effect.
Link: http://lkml.kernel.org/r/CAHk-=whC6Ji=fWnjh2+eS4b15TnbsS4VPVtvBOwCy1jjEG_JHQ@mail.gmail.com
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Running the latest kernel through my "make instances" stress tests, I
triggered the following bug (with KASAN and kmemleak enabled):
mkdir invoked oom-killer:
gfp_mask=0x40cd0(GFP_KERNEL|__GFP_COMP|__GFP_RECLAIMABLE), order=0,
oom_score_adj=0
CPU: 1 PID: 2229 Comm: mkdir Not tainted 5.4.0-rc2-test #325
Hardware name: MSI MS-7823/CSM-H87M-G43 (MS-7823), BIOS V1.6 02/22/2014
Call Trace:
dump_stack+0x64/0x8c
dump_header+0x43/0x3b7
? trace_hardirqs_on+0x48/0x4a
oom_kill_process+0x68/0x2d5
out_of_memory+0x2aa/0x2d0
__alloc_pages_nodemask+0x96d/0xb67
__alloc_pages_node+0x19/0x1e
alloc_slab_page+0x17/0x45
new_slab+0xd0/0x234
___slab_alloc.constprop.86+0x18f/0x336
? alloc_inode+0x2c/0x74
? irq_trace+0x12/0x1e
? tracer_hardirqs_off+0x1d/0xd7
? __slab_alloc.constprop.85+0x21/0x53
__slab_alloc.constprop.85+0x31/0x53
? __slab_alloc.constprop.85+0x31/0x53
? alloc_inode+0x2c/0x74
kmem_cache_alloc+0x50/0x179
? alloc_inode+0x2c/0x74
alloc_inode+0x2c/0x74
new_inode_pseudo+0xf/0x48
new_inode+0x15/0x25
tracefs_get_inode+0x23/0x7c
? lookup_one_len+0x54/0x6c
tracefs_create_file+0x53/0x11d
trace_create_file+0x15/0x33
event_create_dir+0x2a3/0x34b
__trace_add_new_event+0x1c/0x26
event_trace_add_tracer+0x56/0x86
trace_array_create+0x13e/0x1e1
instance_mkdir+0x8/0x17
tracefs_syscall_mkdir+0x39/0x50
? get_dname+0x31/0x31
vfs_mkdir+0x78/0xa3
do_mkdirat+0x71/0xb0
sys_mkdir+0x19/0x1b
do_fast_syscall_32+0xb0/0xed
I bisected this down to the addition of the proxy_ops into tracefs for
lockdown. It appears that the allocation of the proxy_ops and then freeing
it in the destroy_inode callback, is causing havoc with the memory system.
Reading the documentation about destroy_inode and talking with Linus about
this, this is buggy and wrong. When defining the destroy_inode() method, it
is expected that the destroy_inode() will also free the inode, and not just
the extra allocations done in the creation of the inode. The faulty commit
causes a memory leak of the inode data structure when they are deleted.
Instead of allocating the proxy_ops (and then having to free it) the checks
should be done by the open functions themselves, and not hack into the
tracefs directory. First revert the tracefs updates for locked_down and then
later we can add the locked_down checks in the kernel/trace files.
Link: http://lkml.kernel.org/r/20191011135458.7399da44@gandalf.local.home
Fixes: ccbd54ff54 ("tracefs: Restrict tracefs when the kernel is locked down")
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Pull kernel lockdown mode from James Morris:
"This is the latest iteration of the kernel lockdown patchset, from
Matthew Garrett, David Howells and others.
From the original description:
This patchset introduces an optional kernel lockdown feature,
intended to strengthen the boundary between UID 0 and the kernel.
When enabled, various pieces of kernel functionality are restricted.
Applications that rely on low-level access to either hardware or the
kernel may cease working as a result - therefore this should not be
enabled without appropriate evaluation beforehand.
The majority of mainstream distributions have been carrying variants
of this patchset for many years now, so there's value in providing a
doesn't meet every distribution requirement, but gets us much closer
to not requiring external patches.
There are two major changes since this was last proposed for mainline:
- Separating lockdown from EFI secure boot. Background discussion is
covered here: https://lwn.net/Articles/751061/
- Implementation as an LSM, with a default stackable lockdown LSM
module. This allows the lockdown feature to be policy-driven,
rather than encoding an implicit policy within the mechanism.
The new locked_down LSM hook is provided to allow LSMs to make a
policy decision around whether kernel functionality that would allow
tampering with or examining the runtime state of the kernel should be
permitted.
The included lockdown LSM provides an implementation with a simple
policy intended for general purpose use. This policy provides a coarse
level of granularity, controllable via the kernel command line:
lockdown={integrity|confidentiality}
Enable the kernel lockdown feature. If set to integrity, kernel features
that allow userland to modify the running kernel are disabled. If set to
confidentiality, kernel features that allow userland to extract
confidential information from the kernel are also disabled.
This may also be controlled via /sys/kernel/security/lockdown and
overriden by kernel configuration.
New or existing LSMs may implement finer-grained controls of the
lockdown features. Refer to the lockdown_reason documentation in
include/linux/security.h for details.
The lockdown feature has had signficant design feedback and review
across many subsystems. This code has been in linux-next for some
weeks, with a few fixes applied along the way.
Stephen Rothwell noted that commit 9d1f8be5cf ("bpf: Restrict bpf
when kernel lockdown is in confidentiality mode") is missing a
Signed-off-by from its author. Matthew responded that he is providing
this under category (c) of the DCO"
* 'next-lockdown' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security: (31 commits)
kexec: Fix file verification on S390
security: constify some arrays in lockdown LSM
lockdown: Print current->comm in restriction messages
efi: Restrict efivar_ssdt_load when the kernel is locked down
tracefs: Restrict tracefs when the kernel is locked down
debugfs: Restrict debugfs when the kernel is locked down
kexec: Allow kexec_file() with appropriate IMA policy when locked down
lockdown: Lock down perf when in confidentiality mode
bpf: Restrict bpf when kernel lockdown is in confidentiality mode
lockdown: Lock down tracing and perf kprobes when in confidentiality mode
lockdown: Lock down /proc/kcore
x86/mmiotrace: Lock down the testmmiotrace module
lockdown: Lock down module params that specify hardware parameters (eg. ioport)
lockdown: Lock down TIOCSSERIAL
lockdown: Prohibit PCMCIA CIS storage when the kernel is locked down
acpi: Disable ACPI table override if the kernel is locked down
acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down
ACPI: Limit access to custom_method when the kernel is locked down
x86/msr: Restrict MSR access when the kernel is locked down
x86: Lock down IO port access when the kernel is locked down
...
Tracefs may release more information about the kernel than desirable, so
restrict it when the kernel is locked down in confidentiality mode by
preventing open().
(Fixed by Ben Hutchings to avoid a null dereference in
default_file_open())
Signed-off-by: Matthew Garrett <mjg59@google.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: James Morris <jmorris@namei.org>
This will allow generating fsnotify delete events after the
fsnotify_nameremove() hook is removed from d_delete().
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Based on 2 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license version 2 as
published by the free software foundation #
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 4122 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Enrico Weigelt <info@metux.net>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Add SPDX license identifiers to all Make/Kconfig files which:
- Have no license information of any form
These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:
GPL-2.0-only
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
tracefs_ops is initialized inside tracefs_create_instance_dir and not
modified after. tracefs_create_instance_dir allows for initialization
only once, and is called from create_trace_instances(marked __init),
which is called from tracer_init_tracefs(marked __init). Also, mark
tracefs_create_instance_dir as __init.
Link: http://lkml.kernel.org/r/20180725171901.4468-1-zsm@chromium.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Zubin Mithra <zsm@chromium.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
btrfs, debugfs, reiserfs and tracefs call save_mount_options() and reiserfs
calls replace_mount_options(), but they then implement their own
->show_options() methods and don't touch s_options, rendering the saved
options unnecessary. I'm trying to eliminate s_options to make it easier
to implement a context-based mount where the mount options can be passed
individually over a file descriptor.
Remove the calls to save/replace_mount_options() call in these cases.
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Chris Mason <clm@fb.com>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
cc: Steven Rostedt <rostedt@goodmis.org>
cc: linux-btrfs@vger.kernel.org
cc: reiserfs-devel@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
simple_fill_super() is passed an array of tree_descr structures which
describe the files to create in the filesystem's root directory. Since
these arrays are never modified intentionally, they should be 'const' so
that they are placed in .rodata and benefit from memory protection.
This patch updates the function signature and all users, and also
constifies tree_descr.name.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
CURRENT_TIME macro is not appropriate for filesystems as it
doesn't use the right granularity for filesystem timestamps.
Use current_time() instead.
CURRENT_TIME is also not y2038 safe.
This is also in preparation for the patch that transitions
vfs timestamps to use 64 bit time and hence make them
y2038 safe. As part of the effort current_time() will be
extended to do range checks. Hence, it is necessary for all
file system timestamps to use current_time(). Also,
current_time() will be transitioned along with vfs to be
y2038 safe.
Note that whenever a single call to current_time() is used
to change timestamps in different inodes, it is because they
share the same time granularity.
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Felipe Balbi <balbi@kernel.org>
Acked-by: Steven Whitehouse <swhiteho@redhat.com>
Acked-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Acked-by: David Sterba <dsterba@suse.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).
Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
In tracefs' start_creating(), we pin the file system to safely access
its root. When we failed to create a file, we unpin the file system via
failed_creating() to release the mount count and eventually the reference
of the singleton vfsmount.
However, when we run into an error during lookup_one_len() when still
in start_creating(), we only release the parent's mutex but not so the
reference on the mount.
F.e., in securityfs_create_file(), after doing simple_pin_fs() when
lookup_one_len() fails there, we infact do simple_release_fs(). This
seems necessary here as well.
Same issue seen in debugfs due to 190afd81e4 ("debugfs: split the
beginning and the end of __create_file() off"), which seemed to got
carried over into tracefs, too. Noticed during code review.
Link: http://lkml.kernel.org/r/68efa86101b778cf7517ed7c6ad573bd69f60ec6.1446672850.git.daniel@iogearbox.net
Fixes: 4282d60689 ("tracefs: Add new tracefs file system")
Cc: stable@vger.kernel.org # 4.1+
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Pull more vfs updates from Al Viro:
"Assorted VFS fixes and related cleanups (IMO the most interesting in
that part are f_path-related things and Eric's descriptor-related
stuff). UFS regression fixes (it got broken last cycle). 9P fixes.
fs-cache series, DAX patches, Jan's file_remove_suid() work"
[ I'd say this is much more than "fixes and related cleanups". The
file_table locking rule change by Eric Dumazet is a rather big and
fundamental update even if the patch isn't huge. - Linus ]
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (49 commits)
9p: cope with bogus responses from server in p9_client_{read,write}
p9_client_write(): avoid double p9_free_req()
9p: forgetting to cancel request on interrupted zero-copy RPC
dax: bdev_direct_access() may sleep
block: Add support for DAX reads/writes to block devices
dax: Use copy_from_iter_nocache
dax: Add block size note to documentation
fs/file.c: __fget() and dup2() atomicity rules
fs/file.c: don't acquire files->file_lock in fd_install()
fs:super:get_anon_bdev: fix race condition could cause dev exceed its upper limitation
vfs: avoid creation of inode number 0 in get_next_ino
namei: make set_root_rcu() return void
make simple_positive() public
ufs: use dir_pages instead of ufs_dir_pages()
pagemap.h: move dir_pages() over there
remove the pointless include of lglock.h
fs: cleanup slight list_entry abuse
xfs: Correctly lock inode when removing suid and file capabilities
fs: Call security_ops->inode_killpriv on truncate
fs: Provide function telling whether file_remove_privs() will do anything
...
This allows for better documentation in the code and
it allows for a simpler and fully correct version of
fs_fully_visible to be written.
The mount points converted and their filesystems are:
/sys/hypervisor/s390/ s390_hypfs
/sys/kernel/config/ configfs
/sys/kernel/debug/ debugfs
/sys/firmware/efi/efivars/ efivarfs
/sys/fs/fuse/connections/ fusectl
/sys/fs/pstore/ pstore
/sys/kernel/tracing/ tracefs
/sys/fs/cgroup/ cgroup
/sys/kernel/security/ securityfs
/sys/fs/selinux/ selinuxfs
/sys/fs/smackfs/ smackfs
Cc: stable@vger.kernel.org
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
The tracing "instances" directory can create sub tracing buffers
with mkdir, and remove them with rmdir. As a mkdir will also create
all the files and directories that control the sub buffer the inode
mutexes need to be released before this is done, to avoid deadlocks.
It is better to let the tracing system unlock the inode mutexes before
calling the functions that create the files within the new directory
(or deletes the files from the one being destroyed).
Now that tracing has been converted over to tracefs, the tracefs file
system can be modified to accommodate this feature. It still releases
the locks, but the filesystem itself can take care of the ugly
business and let the user just do what it needs.
The tracing system now attaches a descriptor to the directory dentry
that can have userspace create or remove sub directories. If this
descriptor does not exist for a dentry, then that dentry can not be
used to create other directories. This descriptor holds a mkdir and
rmdir method that only takes a character string as an argument.
The tracefs file system will first make a copy of the dentry name
before releasing the locks. Then it will pass the copied name to the
methods. It is up to the tracing system that supplied the methods to
handle races with duplicate names and such as all the inode mutexes
would be released when the functions are called.
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
When tracefs is configured, have the directory /sys/kernel/tracing appear
just like /sys/kernel/debug appears when debugfs is configured.
This will give a consistent place for system admins to mount tracefs.
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Add a separate file system to handle the tracing directory. Currently it
is part of debugfs, but that is starting to show its limits.
One thing is that in order to access the tracing infrastructure, you need
to mount debugfs. As that includes debugging from all sorts of sub systems
in the kernel, it is not considered advisable to mount such an all
encompassing debugging system.
Having the tracing system in its own file systems gives access to the
tracing sub system without needing to include all other systems.
Another problem with tracing using the debugfs system is that the
instances use mkdir to create sub buffers. debugfs does not support mkdir
from userspace so to implement it, special hacks were used. By controlling
the file system that the tracing infrastructure uses, this can be properly
done without hacks.
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
