From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8EDEE11713; Fri, 26 Sep 2025 10:00:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758880834; cv=none; b=VwtPG2fj2sznvlabX9Qeeww+DGWN/I2UoIkcJM590sQ/dI8YdYRGSHzpixvn4LitCvHybtxEPBJO6hRAid9tDyHujBdytH8e7AerVCmFnIwoKRy+sgoLBX/WdJifB2AQkBIpkaZvASfFm5R7+YdJiXuOEtpzYhRiIDfBSXp/LHg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758880834; c=relaxed/simple; bh=1aIJrKPq5VQMrWvrNmT6PAyofISX8JoKSfH7dSwgH14=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=vAO5X8XpPTkJYLah57pU2szLe4NTRVWAih5ufcGmC8WNKnKNsr4YGtz/zZ+iIcxFPc1H9ojY5VfdVQCD+y9mB/bxxMSZd4GlXZSauqvteN8mQbkQDxxR+7ePyagE8CSjAWeuvXhdIpacT6Sum8IZKFE7nrASUe0P+Ra+x+OEV4A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=q/3KzJVd; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="q/3KzJVd" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9EFF5C4CEF4; Fri, 26 Sep 2025 10:00:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758880834; bh=1aIJrKPq5VQMrWvrNmT6PAyofISX8JoKSfH7dSwgH14=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=q/3KzJVdT6fepxi9RcbaGv5ahZVFQj4EIKNvoLQm0Rsd/1cvrwnfvsv/2bCwARDDE peUMx6yVMmcCNj9gEsDk4AfL7lQhs6K4VyVX5Bxzb0THZ/1BEev+LRz4m9iNpN2pVV SYDutsoVLAZulCWho3myKPE6M8kr4psk3M3AUpFQHs+p9D0iDUTrrqHi5y2MeNngY9 +uH2M+s2pJmE2kbxX5fHTu6Fsjx0n+0T6KaYbym6Lqia4sUIyESxJjYj9t+qjweiPT K8MJG/5BGk56SyBqU6gr2YPFe2crwU3llTUwXDwDNNDBFHVGhNvX7Od1ULrJH0Guh3 LvM8n0VKDi4Zg== Message-ID: Subject: Re: [RFC PATCH] fs: Plumb case sensitivity bits into statx From: Jeff Layton To: Chuck Lever , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Cc: Chuck Lever , Volker Lendecke Date: Fri, 26 Sep 2025 06:00:32 -0400 In-Reply-To: <20250925151140.57548-1-cel@kernel.org> References: <20250925151140.57548-1-cel@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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about the case sensitivity and case preservation behaviors > of shared file systems. Today, the Linux NFSD implementation > unconditionally returns "the export is case sensitive and case > preserving". >=20 > However, a few Linux in-tree file system types appear to have some > ability to handle case-folded filenames. Some of our users would > like to exploit that functionality from their non-POSIX NFS clients. >=20 > Enable upper layers such as NFSD to retrieve case sensitivity > information from file systems by adding a statx API for this > purpose. Introduce a sample producer and a sample consumer for this > information. >=20 > If this mechanism seems sensible, a future patch might add a similar > field to the user-space-visible statx structure. User-space file > servers already use a variety of APIs to acquire this information. >=20 > Suggested-by: Jeff Layton > Cc: Volker Lendecke > Signed-off-by: Chuck Lever > --- > fs/fat/file.c | 5 +++++ > fs/nfsd/nfs3proc.c | 35 +++++++++++++++++++++++++++-------- > include/linux/stat.h | 1 + > include/uapi/linux/stat.h | 15 +++++++++++++++ > 4 files changed, 48 insertions(+), 8 deletions(-) >=20 > I'm certain this RFC patch has a number of problems, but it should > serve as a discussion point. >=20 >=20 > diff --git a/fs/fat/file.c b/fs/fat/file.c > index 4fc49a614fb8..8572e36d8f27 100644 > --- a/fs/fat/file.c > +++ b/fs/fat/file.c > @@ -413,6 +413,11 @@ int fat_getattr(struct mnt_idmap *idmap, const struc= t path *path, > stat->result_mask |=3D STATX_BTIME; > stat->btime =3D MSDOS_I(inode)->i_crtime; > } > + if (request_mask & STATX_CASE_INFO) { > + stat->result_mask |=3D STATX_CASE_INFO; > + /* STATX_CASE_PRESERVING is cleared */ > + stat->case_info =3D statx_case_ascii; > + } > =20 > return 0; > } > diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c > index b6d03e1ef5f7..b319d1c4385c 100644 > --- a/fs/nfsd/nfs3proc.c > +++ b/fs/nfsd/nfs3proc.c > @@ -697,6 +697,31 @@ nfsd3_proc_fsinfo(struct svc_rqst *rqstp) > return rpc_success; > } > =20 > +static __be32 > +nfsd3_proc_case(struct svc_fh *fhp, struct nfsd3_pathconfres *resp) > +{ > + struct path p =3D { > + .mnt =3D fhp->fh_export->ex_path.mnt, > + .dentry =3D fhp->fh_dentry, > + }; > + u32 request_mask =3D STATX_CASE_INFO; > + struct kstat stat; > + __be32 nfserr; > + > + nfserr =3D nfserrno(vfs_getattr(&p, &stat, request_mask, > + AT_STATX_SYNC_AS_STAT)); > + if (nfserr !=3D nfs_ok) > + return nfserr; > + if (!(stat.result_mask & STATX_CASE_INFO)) > + return nfs_ok; > + > + resp->p_case_insensitive =3D > + stat.case_info & STATX_CASE_FOLDING_TYPE ? 0 : 1; > + resp->p_case_preserving =3D > + stat.case_info & STATX_CASE_PRESERVING ? 1 : 0; > + return nfs_ok; > +} > + > /* > * Get pathconf info for the specified file > */ > @@ -722,17 +747,11 @@ nfsd3_proc_pathconf(struct svc_rqst *rqstp) > if (resp->status =3D=3D nfs_ok) { > struct super_block *sb =3D argp->fh.fh_dentry->d_sb; > =20 > - /* Note that we don't care for remote fs's here */ > - switch (sb->s_magic) { > - case EXT2_SUPER_MAGIC: > + if (sb->s_magic =3D=3D EXT2_SUPER_MAGIC) { > resp->p_link_max =3D EXT2_LINK_MAX; > resp->p_name_max =3D EXT2_NAME_LEN; > - break; > - case MSDOS_SUPER_MAGIC: > - resp->p_case_insensitive =3D 1; > - resp->p_case_preserving =3D 0; > - break; > } > + resp->status =3D nfsd3_proc_case(&argp->fh, resp); > } > =20 > fh_put(&argp->fh); > diff --git a/include/linux/stat.h b/include/linux/stat.h > index e3d00e7bb26d..abb47cbb233a 100644 > --- a/include/linux/stat.h > +++ b/include/linux/stat.h > @@ -59,6 +59,7 @@ struct kstat { > u32 atomic_write_unit_max; > u32 atomic_write_unit_max_opt; > u32 atomic_write_segments_max; > + u32 case_info; > }; > =20 > /* These definitions are internal to the kernel for now. Mainly used by = nfsd. */ > diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h > index 1686861aae20..e929b30d64b6 100644 > --- a/include/uapi/linux/stat.h > +++ b/include/uapi/linux/stat.h > @@ -219,6 +219,7 @@ struct statx { > #define STATX_SUBVOL 0x00008000U /* Want/got stx_subvol */ > #define STATX_WRITE_ATOMIC 0x00010000U /* Want/got atomic_write_* fields= */ > #define STATX_DIO_READ_ALIGN 0x00020000U /* Want/got dio read alignment = info */ > +#define STATX_CASE_INFO 0x00040000U /* Want/got case folding info */ >=20 >=20 Do you intend to expose this new attribute to userland? If not, then it should probably snuggle up next to STATX_CHANGE_COOKIE. If so, then you need to claim a field for it in struct statx, and populate it. I'll also note that you're not using a lot of the bits in this field, and struct statx has a 16-bit spare field next to stx_mode. You may want to rework this to use a 16 bit field and expose it to userland there. > =20 > #define STATX__RESERVED 0x80000000U /* Reserved for future struct statx= expansion */ > =20 > @@ -257,4 +258,18 @@ struct statx { > #define STATX_ATTR_WRITE_ATOMIC 0x00400000 /* File supports atomic writ= e operations */ > =20 > =20 > +/* > + * File system support for case folding is available via a bitmap. > + */ > +#define STATX_CASE_PRESERVING 0x80000000 /* File name case is preserved= */ > + > +/* Values stored in the low-order byte of .case_info */ > +enum { > + statx_case_sensitive =3D 0, > + statx_case_ascii, > + statx_case_utf8, > + statx_case_utf16, > +}; These all need _very_ clear definitions, especially if you're exposing this to userland. The devil is in the details when it comes to casefolding and there is not a lot of consistency across filesystems. The callers need to know what they can expect when they see that these bits are set. > +#define STATX_CASE_FOLDING_TYPE 0x000000ff > + > #endif /* _UAPI_LINUX_STAT_H */ =20 --=20 Jeff Layton