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

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Message-ID: <c3b285b0-33d1-4bfa-b8ab-6783ff5ed78d@quicinc.com>
Date: Thu, 21 Nov 2024 12:12:17 +0530
From: Ekansh Gupta <quic_ekangupt@...cinc.com>
To: Greg KH <gregkh@...uxfoundation.org>
CC: <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 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.

Do you suggest that looking up the name is a better approach that saving
the file?
>
>> +		kfree(debugfs_buf);
>> +	}
>> +}
>> +
>> +void fastrpc_remove_user_debugfs(struct fastrpc_user *fl)
>> +{
>> +	debugfs_remove(fl->debugfs_file);
> Why remove just the file and not the whole directory?
As mentioned above, file process specific and is getting created when
any process uses fastrpc driver. It is getting deleted when the process
releases the device.
>
>> +}
>> +
>> +struct dentry *fastrpc_create_debugfs_dir(const char *name)
>> +{
>> +	return debugfs_create_dir(name, NULL);
> At the root of debugfs?  Why is this function even needed?
creating a dir named "fastrpc_adsp", "fastrpc_cdsp" etc. to create debugfs
file for the processes using adsp, cdsp etc.
>
>> +}
>> +
>> +void fastrpc_remove_debugfs_dir(struct dentry *cctx_debugfs)
>> +{
>> +	debugfs_remove_recursive(cctx_debugfs);
> See, you don't need the debugfs file reference at all, you don't do
> anything with it.
right, I can try with look up.
> And again, why are you wrapping basic debugfs functions with your own
> version?  Please don't do that.
Ack. Thanks for reviewing this change.

--ekansh
>
> thanks,
>
> greg k-h