kernel/linux.git/fs/filesystems.c, branch v7.2-rc1

fs: fix ups and tidy ups to /proc/filesystems caching

2026-06-12T12:26:27+00:00

- add missing unlocks in some corner cases - whitespace touch ups - s/smp_store_release/rcu_assign_pointer/ [nop, the macro expands to the same thing] - mark file_systems_string as __read_mostly Signed-off-by: Mateusz Guzik Link: https://patch.msgid.link/20260610143954.34185-1-mjguzik@gmail.com Signed-off-by: Christian Brauner (Amutable)

fs: cache the string generated by reading /proc/filesystems

2026-05-11T21:13:01+00:00

It is being read surprisingly often (e.g., by mkdir, ls and even sed!). This is lock-protected pointer chasing over a linked list to pay for sprintf for every fs (32 on my boxen). Instead cache the result. While here make the file as permanent to avoid spurious ref trips in procfs. Signed-off-by: Mateusz Guzik Link: https://patch.msgid.link/20260425220844.1763933-4-mjguzik@gmail.com Signed-off-by: Christian Brauner

fs: RCU-ify filesystems list

2026-05-11T21:13:01+00:00

The drivers list was protected by an rwlock; every mount, every open of /proc/filesystems and the legacy sysfs(2) syscall walked a hand-rolled singly-linked list under it. /proc/filesystems is especially hot because libselinux causes programs as mundane as mkdir, ls and sed to open and read it on every invocation. Convert the list to an RCU-protected hlist and switch the writer side to a plain spinlock. Writers keep their existing non-sleeping section while readers walk under rcu_read_lock() with no lock traffic: - register_filesystem()/unregister_filesystem() take file_systems_lock, publish via hlist_{add_tail,del_init}_rcu() and invalidate the cached /proc/filesystems string. unregister_filesystem() keeps its synchronize_rcu() after dropping the lock so in-flight readers are drained before the module (and its embedded file_system_type) can go away. - __get_fs_type(), list_bdev_fs_names() and the fs_index()/fs_name()/fs_maxindex() helpers walk the list under rcu_read_lock(). fs_name() continues to drop the read-side lock after try_module_get() and accesses ->name outside the RCU section; the module reference pins the embedded file_system_type across the boundary. struct file_system_type::next becomes struct hlist_node list; no in-tree caller references the old ->next field outside fs/filesystems.c. Link: https://patch.msgid.link/20260425220844.1763933-3-mjguzik@gmail.com Signed-off-by: Christian Brauner

sysfs(2): fs_index() argument is _not_ a pathname

2026-01-16T17:52:04+00:00

... it's a filesystem type name. Signed-off-by: Al Viro

fs/filesystems: Fix potential unsigned integer underflow in fs_name()

2025-04-14T11:05:59+00:00

fs_name() has @index as unsigned int, so there is underflow risk for operation '@index--'. Fix by breaking the for loop when '@index == 0' which is also more proper than '@index <= 0' for unsigned integer comparison. Signed-off-by: Zijun Hu Link: https://lore.kernel.org/20250410-fix_fs-v1-1-7c14ccc8ebaa@quicinc.com Signed-off-by: Christian Brauner

fs: simplify get_filesystem_list / get_all_fs_names

2021-08-23T05:25:40+00:00

Just output the '\0' separate list of supported file systems for block devices directly rather than going through a pointless round of string manipulation. Based on an earlier patch from Al Viro . Vivek: Modified list_bdev_fs_names() and split_fs_names() to return number of null terminted strings to caller. Callers now use that information to loop through all the strings instead of relying on one extra null char being present at the end. Signed-off-by: Christoph Hellwig Signed-off-by: Vivek Goyal Signed-off-by: Al Viro

fs/filesystems.c: downgrade user-reachable WARN_ONCE() to pr_warn_once()

2020-04-10T22:36:22+00:00

After request_module(), nothing is stopping the module from being unloaded until someone takes a reference to it via try_get_module(). The WARN_ONCE() in get_fs_type() is thus user-reachable, via userspace running 'rmmod' concurrently. Since WARN_ONCE() is for kernel bugs only, not for user-reachable situations, downgrade this warning to pr_warn_once(). Keep it printed once only, since the intent of this warning is to detect a bug in modprobe at boot time. Printing the warning more than once wouldn't really provide any useful extra information. Fixes: 41124db869b7 ("fs: warn in case userspace lied about modprobe return") Signed-off-by: Eric Biggers Signed-off-by: Andrew Morton Reviewed-by: Jessica Yu Cc: Alexei Starovoitov Cc: Greg Kroah-Hartman Cc: Jeff Vander Stoep Cc: Jessica Yu Cc: Kees Cook Cc: Luis Chamberlain Cc: NeilBrown Cc: [4.13+] Link: http://lkml.kernel.org/r/20200312202552.241885-3-ebiggers@kernel.org Signed-off-by: Linus Torvalds

fs_parser: remove fs_parameter_description name field

2020-02-07T19:48:36+00:00

Unused now. Signed-off-by: Eric Sandeen Acked-by: David Howells Signed-off-by: Al Viro

vfs: Implement a filesystem superblock creation/configuration context

2019-02-28T08:29:26+00:00

[AV - unfuck kern_mount_data(); we want non-NULL ->mnt_ns on long-living mounts] [AV - reordering fs/namespace.c is badly overdue, but let's keep it separate from that series] [AV - drop simple_pin_fs() change] [AV - clean vfs_kern_mount() failure exits up] Implement a filesystem context concept to be used during superblock creation for mount and superblock reconfiguration for remount. The mounting procedure then becomes: (1) Allocate new fs_context context. (2) Configure the context. (3) Create superblock. (4) Query the superblock. (5) Create a mount for the superblock. (6) Destroy the context. Rather than calling fs_type->mount(), an fs_context struct is created and fs_type->init_fs_context() is called to set it up. Pointers exist for the filesystem and LSM to hang their private data off. A set of operations has to be set by ->init_fs_context() to provide freeing, duplication, option parsing, binary data parsing, validation, mounting and superblock filling. Legacy filesystems are supported by the provision of a set of legacy fs_context operations that build up a list of mount options and then invoke fs_type->mount() from within the fs_context ->get_tree() operation. This allows all filesystems to be accessed using fs_context. It should be noted that, whilst this patch adds a lot of lines of code, there is quite a bit of duplication with existing code that can be eliminated should all filesystems be converted over. Signed-off-by: David Howells Signed-off-by: Al Viro

proc: introduce proc_create_single{,_data}

2018-05-16T05:23:35+00:00

Variants of proc_create{,_data} that directly take a seq_file show callback and drastically reduces the boilerplate code in the callers. All trivial callers converted over. Signed-off-by: Christoph Hellwig