Re: [PATCH bpf-next 1/3] bpf: Add bpf_path_getattr()

[bot+bpf-ci]

> bpf: Add bpf_path_getattr()

TL;DR: Design nit only: bpf_path_getattr() near-copies the mount ID and
mount-root handling from vfs_statx_path(), so the two may drift; suggests a
shared helper in fs/stat.c and avoiding VFS-private headers.

> diff --git a/fs/bpf_fs_kfuncs.c b/fs/bpf_fs_kfuncs.c
> index 35ccd98a4de6..95d7b0de2453 100644
> --- a/fs/bpf_fs_kfuncs.c
> +++ b/fs/bpf_fs_kfuncs.c

[ ... ]

> @@ -1,23 +1,127 @@
>  #include <linux/xattr.h>
>  
> +#include "internal.h"
> +#include "mount.h"
> +

[ ... ]

> +	if (request_mask & STATX_MNT_ID_UNIQUE) {
> +		out->mnt_id = real_mount(path->mnt)->mnt_id_unique;
> +		stat.result_mask |= STATX_MNT_ID_UNIQUE;
> +	} else {
> +		out->mnt_id = real_mount(path->mnt)->mnt_id;
> +		stat.result_mask |= STATX_MNT_ID;
> +	}
> +	out->size = stat.size;
> +	out->attributes = stat.attributes & ~STATX_ATTR_CHANGE_MONOTONIC;
> +	if (path_mounted(path))
> +		out->attributes |= STATX_ATTR_MOUNT_ROOT;
> +	out->attributes_mask = stat.attributes_mask | STATX_ATTR_MOUNT_ROOT;

this isn't a bug, but could the mount ID and STATX_ATTR_MOUNT_ROOT handling
be shared with vfs_statx_path() through a small helper in fs/stat.c?

This block looks like a near-verbatim copy of the post-getattr part of
vfs_statx_path(), plus the STATX_ATTR_CHANGE_MONOTONIC masking from
cp_statx().

The kernel-doc says 'Results follow statx(2)', so a later change to
vfs_statx_path() (a new mount attribute, a different mount ID rule) would
have to be mirrored here by hand.

The copy is also why this file now includes the VFS-private headers:

	#include "internal.h"
	#include "mount.h"

just to reach real_mount() and path_mounted().  A helper in fs/stat.c that
applies the mount ID and mount-root fields to a kstat would keep the two
in sync and keep struct mount inside fs/.


---
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CI run summary: https://github.com/kernel-patches/bpf/actions/runs/40857522501