On Wed, Oct 18, 2023 at 09:25:11AM -0300, Wedson Almeida Filho wrote:
> From: Wedson Almeida Filho <walmeida@xxxxxxxxxxxxx>
>
> Allow Rust file systems to expose their stats. `overlayfs` requires that
> this be implemented by all file systems that are part of an overlay.
> The planned file systems need to be overlayed with overlayfs, so they
> must be able to implement this.
>
> Signed-off-by: Wedson Almeida Filho <walmeida@xxxxxxxxxxxxx>
> ---
> rust/bindings/bindings_helper.h | 1 +
> rust/kernel/error.rs | 1 +
> rust/kernel/fs.rs | 52 ++++++++++++++++++++++++++++++++-
> 3 files changed, 53 insertions(+), 1 deletion(-)
>
> diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
> index fa754c5e85a2..e2b2ccc835e3 100644
> --- a/rust/bindings/bindings_helper.h
> +++ b/rust/bindings/bindings_helper.h
> @@ -11,6 +11,7 @@
> #include <linux/fs.h>
> #include <linux/fs_context.h>
> #include <linux/slab.h>
> +#include <linux/statfs.h>
> #include <linux/pagemap.h>
> #include <linux/refcount.h>
> #include <linux/wait.h>
> diff --git a/rust/kernel/error.rs b/rust/kernel/error.rs
> index 6c167583b275..829756cf6c48 100644
> --- a/rust/kernel/error.rs
> +++ b/rust/kernel/error.rs
> @@ -83,6 +83,7 @@ macro_rules! declare_err {
> declare_err!(ENOGRACE, "NFS file lock reclaim refused.");
> declare_err!(ENODATA, "No data available.");
> declare_err!(EOPNOTSUPP, "Operation not supported on transport endpoint.");
> + declare_err!(ENOSYS, "Invalid system call number.");
> }
>
> /// Generic integer kernel error.
> diff --git a/rust/kernel/fs.rs b/rust/kernel/fs.rs
> index adf9cbee16d2..8f34da50e694 100644
> --- a/rust/kernel/fs.rs
> +++ b/rust/kernel/fs.rs
> @@ -50,6 +50,31 @@ pub trait FileSystem {
> fn read_xattr(_inode: &INode<Self>, _name: &CStr, _outbuf: &mut [u8]) -> Result<usize> {
> Err(EOPNOTSUPP)
> }
> +
> + /// Get filesystem statistics.
> + fn statfs(_sb: &SuperBlock<Self>) -> Result<Stat> {
> + Err(ENOSYS)
> + }
> +}
> +
> +/// File system stats.
> +///
> +/// A subset of C's `kstatfs`.
> +pub struct Stat {
> + /// Magic number of the file system.
> + pub magic: u32,
> +
> + /// The maximum length of a file name.
> + pub namelen: i64,
Yikes, I hope I never see an 8EB filename. The C side doesn't handle
names longer than 255 bytes.
> +
> + /// Block size.
> + pub bsize: i64,
Or an 8EB block size. SMR notwithstanding, I think this could be u32.
Why are these values signed? Nobody has a -1k block filesystem.
> + /// Number of files in the file system.
> + pub files: u64,
> +
> + /// Number of blocks in the file system.
> + pub blocks: u64,
> }
>
> /// The types of directory entries reported by [`FileSystem::read_dir`].
> @@ -478,7 +503,7 @@ impl<T: FileSystem + ?Sized> Tables<T> {
> freeze_fs: None,
> thaw_super: None,
> unfreeze_fs: None,
> - statfs: None,
> + statfs: Some(Self::statfs_callback),
> remount_fs: None,
> umount_begin: None,
> show_options: None,
> @@ -496,6 +521,31 @@ impl<T: FileSystem + ?Sized> Tables<T> {
> shutdown: None,
> };
>
> + unsafe extern "C" fn statfs_callback(
> + dentry: *mut bindings::dentry,
> + buf: *mut bindings::kstatfs,
> + ) -> core::ffi::c_int {
> + from_result(|| {
> + // SAFETY: The C API guarantees that `dentry` is valid for read. `d_sb` is
> + // immutable, so it's safe to read it. The superblock is guaranteed to be valid dor
> + // the duration of the call.
> + let sb = unsafe { &*(*dentry).d_sb.cast::<SuperBlock<T>>() };
> + let s = T::statfs(sb)?;
> +
> + // SAFETY: The C API guarantees that `buf` is valid for read and write.
> + let buf = unsafe { &mut *buf };
> + buf.f_type = s.magic.into();
> + buf.f_namelen = s.namelen;
> + buf.f_bsize = s.bsize;
> + buf.f_files = s.files;
> + buf.f_blocks = s.blocks;
> + buf.f_bfree = 0;
> + buf.f_bavail = 0;
> + buf.f_ffree = 0;
Why is it necessary to fill out the C structure with zeroes?
statfs_by_dentry zeroes the buffer contents before calling ->statfs.
--D
> + Ok(0)
> + })
> + }
> +
> const XATTR_HANDLERS: [*const bindings::xattr_handler; 2] = [&Self::XATTR_HANDLER, ptr::null()];
>
> const XATTR_HANDLER: bindings::xattr_handler = bindings::xattr_handler {
> --
> 2.34.1
>
>
