linux-kernel - Re: [PATCH v1 4/4] misc: fastrpc: Add debugfs support for fastrpc

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Message-ID: <cn7pqvhw4x4y7s5hbgzjpvyjnw4g6hoyepic4jai7x2fjdenxr@ikr4hkorbuwb>
Date: Thu, 21 Nov 2024 20:53:25 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Ekansh Gupta <quic_ekangupt@...cinc.com>
Cc: Greg KH <gregkh@...uxfoundation.org>, srinivas.kandagatla@...aro.org, 
	linux-arm-msm@...r.kernel.org, quic_bkumar@...cinc.com, linux-kernel@...r.kernel.org, 
	quic_chennak@...cinc.com, dri-devel@...ts.freedesktop.org, arnd@...db.de
Subject: Re: [PATCH v1 4/4] misc: fastrpc: Add debugfs support for fastrpc

On Thu, Nov 21, 2024 at 12:12:17PM +0530, Ekansh Gupta wrote:
> 
> 
> On 11/18/2024 7:32 PM, Greg KH wrote:
> > On Mon, Nov 18, 2024 at 02:10:46PM +0530, Ekansh Gupta wrote:
> >> Add changes to support debugfs. The fastrpc directory will be
> >> created which will carry debugfs files for all fastrpc processes.
> >> The information of fastrpc user and channel contexts are getting
> >> captured as part of this change.
> >>
> >> Signed-off-by: Ekansh Gupta <quic_ekangupt@...cinc.com>
> >> ---
> >>  drivers/misc/fastrpc/Makefile        |   3 +-
> >>  drivers/misc/fastrpc/fastrpc_debug.c | 156 +++++++++++++++++++++++++++
> >>  drivers/misc/fastrpc/fastrpc_debug.h |  31 ++++++
> >>  drivers/misc/fastrpc/fastrpc_main.c  |  18 +++-
> >>  4 files changed, 205 insertions(+), 3 deletions(-)
> >>  create mode 100644 drivers/misc/fastrpc/fastrpc_debug.c
> >>  create mode 100644 drivers/misc/fastrpc/fastrpc_debug.h
> >>
> >> diff --git a/drivers/misc/fastrpc/Makefile b/drivers/misc/fastrpc/Makefile
> >> index 020d30789a80..4ff6b64166ae 100644
> >> --- a/drivers/misc/fastrpc/Makefile
> >> +++ b/drivers/misc/fastrpc/Makefile
> >> @@ -1,3 +1,4 @@
> >>  # SPDX-License-Identifier: GPL-2.0
> >>  obj-$(CONFIG_QCOM_FASTRPC)	+= fastrpc.o
> >> -fastrpc-objs	:= fastrpc_main.o
> >> \ No newline at end of file
> >> +fastrpc-objs	:= fastrpc_main.o \
> >> +		fastrpc_debug.o
> > Only build this file if debugfs is enabled.
> >
> > And again, "debug.c"?
> I'll add change to build this only if debugfs is enabled. Going forward I have plans to add
> few more debug specific changes, maybe then I'll need to change the build rules again.
> >
> >> diff --git a/drivers/misc/fastrpc/fastrpc_debug.c b/drivers/misc/fastrpc/fastrpc_debug.c
> >> new file mode 100644
> >> index 000000000000..cdb4fc6845a8
> >> --- /dev/null
> >> +++ b/drivers/misc/fastrpc/fastrpc_debug.c
> >> @@ -0,0 +1,156 @@
> >> +// SPDX-License-Identifier: GPL-2.0
> >> +// Copyright (c) 2024 Qualcomm Innovation Center.
> >> +
> >> +#include <linux/debugfs.h>
> >> +#include <linux/seq_file.h>
> >> +#include "fastrpc_shared.h"
> >> +#include "fastrpc_debug.h"
> >> +
> >> +#ifdef CONFIG_DEBUG_FS
> > Please put the #ifdef in the .h file, not in the .c file.
> Ack
> >
> >> +void fastrpc_create_user_debugfs(struct fastrpc_user *fl)
> >> +{
> >> +	char cur_comm[TASK_COMM_LEN];
> >> +	int domain_id, size;
> >> +	char *debugfs_buf;
> >> +	struct dentry *debugfs_dir = fl->cctx->debugfs_dir;
> >> +
> >> +	memcpy(cur_comm, current->comm, TASK_COMM_LEN);
> >> +	cur_comm[TASK_COMM_LEN-1] = '\0';
> >> +	if (debugfs_dir != NULL) {
> >> +		domain_id = fl->cctx->domain_id;
> >> +		size = snprintf(NULL, 0, "%.10s_%d_%d_%d", cur_comm,
> >> +				current->pid, fl->tgid, domain_id) + 1;
> >> +		debugfs_buf = kzalloc(size, GFP_KERNEL);
> >> +		if (debugfs_buf == NULL)
> >> +			return;
> >> +		/*
> >> +		 * Use HLOS process name, HLOS PID, fastrpc user TGID,
> >> +		 * domain_id in debugfs filename to create unique file name
> >> +		 */
> >> +		snprintf(debugfs_buf, size, "%.10s_%d_%d_%d",
> >> +			cur_comm, current->pid, fl->tgid, domain_id);
> >> +		fl->debugfs_file = debugfs_create_file(debugfs_buf, 0644,
> >> +				debugfs_dir, fl, &fastrpc_debugfs_fops);
> > Why are you saving the debugfs file?  What do you need to do with it
> > that you can't just delete the whole directory, or look up the name
> > again in the future when removing it?
> fl structure is specific to a process using fastrpc driver. The reason to save
> this debugfs file is to delete is when the process releases fastrpc device.
> If the file is not deleted, it might flood multiple files in debugfs directory.
> 
> As part of this change, only the file that is getting created by a process is
> getting removed when process is releasing device and I don't think we
> can clean up the whole directory at this point.

My 2c: it might be better to create a single file that conains
information for all the processes instead of that. Or use fdinfo data to
export process / FD information to userspace.


-- 
With best wishes
Dmitry