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 D0666487BF; Tue, 8 Oct 2024 18:31:54 +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=1728412314; cv=none; b=jvPcVMiSdLIuCLDnn3llyPtznfBEukiqbu9qJhEIFofdhm1es4aZEdrlxQqk1oxHQbH4iisYs+XFf3qgxMYTycUbPvQu/KlQ0nswQb+K8/qMn6YrpN6prQ4T7h5u3hDu2sIMSFk00TMTvbgM73EmR53Doafd3V+DEcOqDE0rXuk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728412314; c=relaxed/simple; bh=gqH7FBABbdqXlfTTq/YBPfcaDVyCpwZuXhPQBMa3CbI=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=cvWcvGuQk9PzhT0F6kLQ3pFrdplOBY7anNLPsbKRlksQr5Ueki2JxTGMs7HTp0vtKQdlKRvCIsK30rHlkX8Q2r4FB6mDGpRpTsnHhk8usM90E83JPm12uSEhCN22L1ZcKycVtbdyOmBUDlS+OtzASKIfxbE8nDRxU6RpyHPzLAY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eVhdBw/t; 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="eVhdBw/t" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F3F85C4CEC7; Tue, 8 Oct 2024 18:31:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728412314; bh=gqH7FBABbdqXlfTTq/YBPfcaDVyCpwZuXhPQBMa3CbI=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=eVhdBw/tUGl4nXIVlFvSWbBDvUtOcx2yzJlev48Sy25YbwlwwNeVCXXEiP2gcCM8y rISOvzu1wI+1vrMKvqkHTs/MxPqhmXJ9MYSt1BcCCHbX2gR7X0g+zyVEGxMCX+jKrv Cmbo/eNwWkgMaVU4mJtLFzcJwYgIZNyin3vV7Zb8ZkwW6FAW3CN7hKZzOoA3ejE+Ws lSpv8DP0NIGS+pYzPhZIV7IZfK15JcehTs/KXchGiW7TMF8sSFIWBs88MN+VPJDnX8 XO+zHSoPBHJIH53uik3FZf1G0BuYkDDL8J8pAnHI/q4mUn1o4HrocYz6ZFln1gBmTy 1SplazI8rdcJg== Message-ID: Subject: Re: [PATCH v3 2/3] fs: name_to_handle_at() support for "explicit connectable" file handles From: Jeff Layton To: Amir Goldstein Cc: Christian Brauner , Jan Kara , Aleksa Sarai , Chuck Lever , linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org Date: Tue, 08 Oct 2024 14:31:52 -0400 In-Reply-To: <20241008152118.453724-3-amir73il@gmail.com> References: <20241008152118.453724-1-amir73il@gmail.com> <20241008152118.453724-3-amir73il@gmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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"connectable" file handles for the subtree_check feature, > which can be resolved to an open file with a connected path. > So far, userspace nfs server could not make use of this functionality. >=20 > Introduce a new flag AT_HANDLE_CONNECTABLE to name_to_handle_at(2). > When used, the encoded file handle is "explicitly connectable". >=20 > The "explicitly connectable" file handle sets bits in the high 16bit of > the handle_type field, so open_by_handle_at(2) will know that it needs > to open a file with a connected path. >=20 > old kernels will now recognize the handle_type with high bits set, > so "explicitly connectable" file handles cannot be decoded by > open_by_handle_at(2) on old kernels. >=20 > The flag AT_HANDLE_CONNECTABLE is not allowed together with either > AT_HANDLE_FID or AT_EMPTY_PATH. >=20 > Signed-off-by: Amir Goldstein > --- > fs/fhandle.c | 48 ++++++++++++++++++++++++++++++++++---- > include/linux/exportfs.h | 2 ++ > include/uapi/linux/fcntl.h | 1 + > 3 files changed, 46 insertions(+), 5 deletions(-) >=20 > diff --git a/fs/fhandle.c b/fs/fhandle.c > index c5792cf3c6e9..7b4c8945efcb 100644 > --- a/fs/fhandle.c > +++ b/fs/fhandle.c > @@ -31,6 +31,14 @@ static long do_sys_name_to_handle(const struct path *p= ath, > if (!exportfs_can_encode_fh(path->dentry->d_sb->s_export_op, fh_flags)) > return -EOPNOTSUPP; > =20 > + /* > + * A request to encode a connectable handle for a disconnected dentry > + * is unexpected since AT_EMPTY_PATH is not allowed. > + */ > + if (fh_flags & EXPORT_FH_CONNECTABLE && > + WARN_ON(path->dentry->d_flags & DCACHE_DISCONNECTED)) > + return -EINVAL; > + Is it possible to get a DCACHE_DISCONNECTED dentry here? This thing comes from a userland path walk (a'la name_to_handle_at()). That means that it necessarily is connected. I'd drop the fh_flags check, since it seems like having that set on any dentry we get in this interface would be a bug. > if (copy_from_user(&f_handle, ufh, sizeof(struct file_handle))) > return -EFAULT; > =20 > @@ -45,7 +53,7 @@ static long do_sys_name_to_handle(const struct path *pa= th, > /* convert handle size to multiple of sizeof(u32) */ > handle_dwords =3D f_handle.handle_bytes >> 2; > =20 > - /* we ask for a non connectable maybe decodeable file handle */ > + /* Encode a possibly decodeable/connectable file handle */ > retval =3D exportfs_encode_fh(path->dentry, > (struct fid *)handle->f_handle, > &handle_dwords, fh_flags); > @@ -67,8 +75,23 @@ static long do_sys_name_to_handle(const struct path *p= ath, > * non variable part of the file_handle > */ > handle_bytes =3D 0; > - } else > + } else { > + /* > + * When asked to encode a connectable file handle, encode this > + * property in the file handle itself, so that we later know > + * how to decode it. > + * For sanity, also encode in the file handle if the encoded > + * object is a directory and verify this during decode, because > + * decoding directory file handles is quite different than > + * decoding connectable non-directory file handles. > + */ > + if (fh_flags & EXPORT_FH_CONNECTABLE) { > + handle->handle_type |=3D FILEID_IS_CONNECTABLE; > + if (d_is_dir(path->dentry)) > + fh_flags |=3D FILEID_IS_DIR; > + } > retval =3D 0; > + } > /* copy the mount id */ > if (unique_mntid) { > if (put_user(real_mount(path->mnt)->mnt_id_unique, > @@ -109,15 +132,30 @@ SYSCALL_DEFINE5(name_to_handle_at, int, dfd, const = char __user *, name, > { > struct path path; > int lookup_flags; > - int fh_flags; > + int fh_flags =3D 0; > int err; > =20 > if (flag & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH | AT_HANDLE_FID | > - AT_HANDLE_MNT_ID_UNIQUE)) > + AT_HANDLE_MNT_ID_UNIQUE | AT_HANDLE_CONNECTABLE)) > + return -EINVAL; > + > + /* > + * AT_HANDLE_FID means there is no intention to decode file handle > + * AT_HANDLE_CONNECTABLE means there is an intention to decode a > + * connected fd (with known path), so these flags are conflicting. > + * AT_EMPTY_PATH could be used along with a dfd that refers to a > + * disconnected non-directory, which cannot be used to encode a > + * connectable file handle, because its parent is unknown. > + */ > + if (flag & AT_HANDLE_CONNECTABLE && > + flag & (AT_HANDLE_FID | AT_EMPTY_PATH)) > return -EINVAL; > + else if (flag & AT_HANDLE_FID) > + fh_flags |=3D EXPORT_FH_FID; > + else if (flag & AT_HANDLE_CONNECTABLE) > + fh_flags |=3D EXPORT_FH_CONNECTABLE; > =20 > lookup_flags =3D (flag & AT_SYMLINK_FOLLOW) ? LOOKUP_FOLLOW : 0; > - fh_flags =3D (flag & AT_HANDLE_FID) ? EXPORT_FH_FID : 0; > if (flag & AT_EMPTY_PATH) > lookup_flags |=3D LOOKUP_EMPTY; > err =3D user_path_at(dfd, name, lookup_flags, &path); > diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h > index 76a3050b3593..230b0e1d669d 100644 > --- a/include/linux/exportfs.h > +++ b/include/linux/exportfs.h > @@ -169,6 +169,8 @@ struct fid { > #define FILEID_USER_FLAGS(type) ((type) & FILEID_USER_FLAGS_MASK) > =20 > /* Flags supported in encoded handle_type that is exported to user */ > +#define FILEID_IS_CONNECTABLE 0x10000 > +#define FILEID_IS_DIR 0x40000 nit: why skip 0x20000 ? > #define FILEID_VALID_USER_FLAGS (0) > =20 > #define FILEID_USER_TYPE_IS_VALID(type) \ > diff --git a/include/uapi/linux/fcntl.h b/include/uapi/linux/fcntl.h > index 87e2dec79fea..56ff2100e021 100644 > --- a/include/uapi/linux/fcntl.h > +++ b/include/uapi/linux/fcntl.h > @@ -153,6 +153,7 @@ > object identity and may not be > usable with open_by_handle_at(2). */ > #define AT_HANDLE_MNT_ID_UNIQUE 0x001 /* Return the u64 unique mount ID.= */ > +#define AT_HANDLE_CONNECTABLE 0x002 /* Request a connectable file handle= */ > =20 > #if defined(__KERNEL__) > #define AT_GETATTR_NOSEC 0x80000000 --=20 Jeff Layton