From nobody Mon Feb 9 07:23:51 2026 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 C239423E35F; Thu, 8 May 2025 08:54:14 +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=1746694454; cv=none; b=jL4SQ2alMdYbzfJtxpVXJ4Eva89LqvNFOj2AarKPJ0xIDKxkz+XLIpvrsKqwd0K3zQyRd1X6djeNaY8FDmum5mTVCB1zJN4v+E6IlattfmmybcgAcZWsQ/GKkz3oqmOoi2jAZWrDEkpwBJCUOHqp//Yrc8C4vK8W/jXjtK3Jhj0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1746694454; c=relaxed/simple; bh=aeZPyyvtHWmKYFfyG8fSOBi9lfDKNm0mWBz3v98X+YA=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=nMmSGuKhfxjIVg6CryYPgrj/GVxALNtG8/ErF9ZEjWUMy+PWv/Xb9c4iUbAaEZYrfUB9gmdG+R0iSrfowSk+SnTvq/rqxHGbNXhtDck15wL2uwhpRRlyvjKY+0rbsmh/t0WjMHFMDInKofC+Poc1E9BROQQB+cAZHxIsRg0qx5g= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=exnMG6s6; 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="exnMG6s6" Received: by smtp.kernel.org (Postfix) with ESMTPS id 5EB9CC4CEEB; Thu, 8 May 2025 08:54:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1746694454; bh=aeZPyyvtHWmKYFfyG8fSOBi9lfDKNm0mWBz3v98X+YA=; h=From:Date:Subject:References:In-Reply-To:To:Cc:Reply-To:From; b=exnMG6s67MADw4z/6O6OIxZLxHzLJd3GTY0zO/Rv8FghMA5cBj6pjXmPk2NochDLh gSFPQN6a8J02CsTvjn8Wgmqd0n5D+bzbvjMgAxYykPxG5NGw7BIG2IrrHAYQSXh0Cg 7MUEooF+sEYTaItGd/30uqweDc+FwYPgOuTUU9G//kgFigrYPG2GqMpYImBe6PVJDK sLCHrtFHJ28JLVqtFGyBriHtWgMZuv02bIh1fbQdvxIZY8wpb8svVqKBWyxSZzPTUq uEP5tEIo2tXRxvG/nZFxN5bXCmErsBuGwcH1f4scK21M4ZeGsYhKcZP2VD0zFe1BIY w3UALKydszhRw== Received: from aws-us-west-2-korg-lkml-1.web.codeaurora.org (localhost.localdomain [127.0.0.1]) by smtp.lore.kernel.org (Postfix) with ESMTP id 510CFC3ABC9; Thu, 8 May 2025 08:54:14 +0000 (UTC) From: Chen Linxuan via B4 Relay Date: Thu, 08 May 2025 16:53:45 +0800 Subject: [PATCH v2 2/3] fs: fuse: add backing_files control file Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250508-fusectl-backing-files-v2-2-62f564e76984@uniontech.com> References: <20250508-fusectl-backing-files-v2-0-62f564e76984@uniontech.com> In-Reply-To: <20250508-fusectl-backing-files-v2-0-62f564e76984@uniontech.com> To: Miklos Szeredi Cc: Amir Goldstein , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Chen Linxuan X-Mailer: b4 0.14.2 X-Developer-Signature: v=1; a=openpgp-sha256; l=6076; i=chenlinxuan@uniontech.com; h=from:subject:message-id; bh=id6oT8a7yC3qd46gYMaegcNojko0bpH3Ayxh7JPrSGg=; b=owEBbQKS/ZANAwAKAXYe5hQ5ma6LAcsmYgBoHHEt1CnQi/e7pwJqkt2cfNBt81LpsAuTZBz42 AhCXSVLg96JAjMEAAEKAB0WIQTO1VElAk6xdvy0ZVp2HuYUOZmuiwUCaBxxLQAKCRB2HuYUOZmu izp6D/oDY1tR3wOwTQg7lSqwVEOAwbsXdkPYA0b4xhU+k4ApVRChlwM/Ud1SnNgsxRGpI6sFu1w abACmc9gNArdAEt/1AcEEhWKdRMLQ2xS06V+++3vr8OSXzuUtLt0eCju5KxpfiEla56OmFVwuhq 1zKGzUxtpjvO31e2iLxG3zoyEyZKvBj4Od9sYP3gC+tgTTyCeeWJlvDn7SqnWnReL4SzT2m5txC VF07yYeefeb+ScTnMUrjSCFxyZYcxQJ+CIqRHGlZWizksDJFw6YxSKloXSYZfXkMJyKfGu7S6OL OyR8U9aUjtzme1RpkHd/q/Jnxyrkbdfpl5qhiX8J6uL7GXbu5oenkJ1yqIW/QePWz8Lt4CUvsc2 DSQEmjdLt9xSArjux2LMmCGCFXbhxPETDU7ivsTbPQ+NVwQbAB1X/RLmiS1WAfiZGjSt/wc1NG4 axFuGMpM0rwFtlYNgKu0WsJiOqexwwLZ1+zsM/MhxygLA1w78oH9GnXVtp13LSPxZ6YUZAFfrEy MapRw9SX6OmS+m3tJsdM8FM5RAK0IiiMdKtYDJefeEfr2EzFYgSAASiqd7g8FKR/LZ9Mfo4qldT ZqBVMH1E+9U2Jt3SaWD5tnlOZWVtno5Rl5vXAbMxM5wgRUjOVlnM7sufVI94ChQ6msnE/iD5LAq UaVvZNNEFOb8hIA== X-Developer-Key: i=chenlinxuan@uniontech.com; a=openpgp; fpr=D818ACDD385CAE92D4BAC01A6269794D24791D21 X-Endpoint-Received: by B4 Relay for chenlinxuan@uniontech.com/default with auth_id=380 X-Original-From: Chen Linxuan Reply-To: chenlinxuan@uniontech.com From: Chen Linxuan Add a new FUSE control file "/sys/fs/fuse/connections/*/backing_files" that exposes the paths of all backing files currently being used in FUSE mount points. This is particularly valuable for tracking and debugging files used in FUSE passthrough mode. This approach is similar to how fixed files in io_uring expose their status through fdinfo, providing administrators with visibility into backing file usage. By making backing files visible through the FUSE control filesystem, administrators can monitor which files are being used for passthrough operations and can force-close them if needed by aborting the connection. This exposure of backing files information is an important step towards potentially relaxing CAP_SYS_ADMIN requirements for certain passthrough operations in the future, allowing for better security analysis of passthrough usage patterns. The control file is implemented using the seq_file interface for efficient handling of potentially large numbers of backing files. Access permissions are set to read-only (0400) as this is an informational interface. FUSE_CTL_NUM_DENTRIES has been increased from 5 to 6 to accommodate the additional control file. Some related discussions can be found at links below. Link: https://lore.kernel.org/all/4b64a41c-6167-4c02-8bae-3021270ca519@fast= mail.fm/T/#mc73e04df56b8830b1d7b06b5d9f22e594fba423e Link: https://lore.kernel.org/linux-fsdevel/CAOQ4uxhAY1m7ubJ3p-A3rSufw_53Wu= DRMT1Zqe_OC0bP_Fb3Zw@mail.gmail.com/ Cc: Amir Goldstein Signed-off-by: Chen Linxuan --- fs/fuse/control.c | 136 ++++++++++++++++++++++++++++++++++++++++++++++++++= +++- fs/fuse/fuse_i.h | 2 +- 2 files changed, 136 insertions(+), 2 deletions(-) diff --git a/fs/fuse/control.c b/fs/fuse/control.c index f0874403b1f7c91571f38e4ae9f8cebe259f7dd1..d1ac934d7b8949577545ffd2053= 5c68a9c4ef90f 100644 --- a/fs/fuse/control.c +++ b/fs/fuse/control.c @@ -11,6 +11,7 @@ #include #include #include +#include =20 #define FUSE_CTL_SUPER_MAGIC 0x65735543 =20 @@ -180,6 +181,136 @@ static ssize_t fuse_conn_congestion_threshold_write(s= truct file *file, return ret; } =20 +struct fuse_backing_files_seq_state { + struct fuse_conn *fc; + int backing_id; +}; + +static void *fuse_backing_files_seq_start(struct seq_file *seq, loff_t *po= s) +{ + struct fuse_backing *fb; + struct fuse_backing_files_seq_state *state; + struct fuse_conn *fc; + int backing_id; + void *ret; + + if (*pos + 1 > INT_MAX) + return ERR_PTR(-EINVAL); + + backing_id =3D *pos + 1; + + fc =3D fuse_ctl_file_conn_get(seq->file); + if (!fc) + return ERR_PTR(-ENOTCONN); + + rcu_read_lock(); + + fb =3D idr_get_next(&fc->backing_files_map, &backing_id); + + rcu_read_unlock(); + + if (!fb) { + ret =3D NULL; + goto err; + } + + state =3D kmalloc(sizeof(*state), GFP_KERNEL); + if (!state) { + ret =3D ERR_PTR(-ENOMEM); + goto err; + } + + state->fc =3D fc; + state->backing_id =3D backing_id; + + ret =3D state; + return ret; + +err: + fuse_conn_put(fc); + return ret; +} + +static void *fuse_backing_files_seq_next(struct seq_file *seq, void *v, + loff_t *pos) +{ + struct fuse_backing_files_seq_state *state =3D v; + struct fuse_backing *fb; + + (*pos)++; + state->backing_id++; + + rcu_read_lock(); + + fb =3D idr_get_next(&state->fc->backing_files_map, &state->backing_id); + + rcu_read_unlock(); + + if (!fb) + return NULL; + + + return state; +} + +static int fuse_backing_files_seq_show(struct seq_file *seq, void *v) +{ + struct fuse_backing_files_seq_state *state =3D v; + struct fuse_conn *fc =3D state->fc; + struct fuse_backing *fb; + + rcu_read_lock(); + + fb =3D idr_find(&fc->backing_files_map, state->backing_id); + fb =3D fuse_backing_get(fb); + if (!fb) + goto out; + + if (!fb->file) + goto out_put_fb; + + seq_printf(seq, "%5u: ", state->backing_id); + seq_file_path(seq, fb->file, " \t\n\\"); + seq_puts(seq, "\n"); + +out_put_fb: + fuse_backing_put(fb); +out: + rcu_read_unlock(); + return 0; +} + +static void fuse_backing_files_seq_stop(struct seq_file *seq, void *v) +{ + struct fuse_backing_files_seq_state *state; + + if (!v) + return; + + state =3D v; + fuse_conn_put(state->fc); + kvfree(state); +} + +static const struct seq_operations fuse_backing_files_seq_ops =3D { + .start =3D fuse_backing_files_seq_start, + .next =3D fuse_backing_files_seq_next, + .stop =3D fuse_backing_files_seq_stop, + .show =3D fuse_backing_files_seq_show, +}; + +static int fuse_backing_files_seq_open(struct inode *inode, struct file *f= ile) +{ + return seq_open(file, &fuse_backing_files_seq_ops); +} + +static const struct file_operations fuse_conn_backing_files_ops =3D { + .open =3D fuse_backing_files_seq_open, + .read =3D seq_read, + .llseek =3D seq_lseek, + .release =3D seq_release, +}; + static const struct file_operations fuse_ctl_abort_ops =3D { .open =3D nonseekable_open, .write =3D fuse_conn_abort_write, @@ -270,7 +401,10 @@ int fuse_ctl_add_conn(struct fuse_conn *fc) 1, NULL, &fuse_conn_max_background_ops) || !fuse_ctl_add_dentry(parent, fc, "congestion_threshold", S_IFREG | 0600, 1, NULL, - &fuse_conn_congestion_threshold_ops)) + &fuse_conn_congestion_threshold_ops) || + !fuse_ctl_add_dentry(parent, fc, "backing_files", S_IFREG | 0400, 1, + NULL, + &fuse_conn_backing_files_ops)) goto err; =20 return 0; diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h index d56d4fd956db99ecd93052a9655428664882cb72..2830b05bb0928e9b30f9905d70f= c3ec1ef11c2a5 100644 --- a/fs/fuse/fuse_i.h +++ b/fs/fuse/fuse_i.h @@ -46,7 +46,7 @@ #define FUSE_NAME_MAX (PATH_MAX - 1) =20 /** Number of dentries for each connection in the control filesystem */ -#define FUSE_CTL_NUM_DENTRIES 5 +#define FUSE_CTL_NUM_DENTRIES 6 =20 /* Frequency (in seconds) of request timeout checks, if opted into */ #define FUSE_TIMEOUT_TIMER_FREQ 15 --=20 2.43.0