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

From: Deepika Singh
Date: Mon Apr 14 2025 - 03:12:31 EST



On 4/11/2025 1:55 PM, Ekansh Gupta wrote:


On 12/3/2024 5:27 PM, Dmitry Baryshkov wrote:
On Tue, 3 Dec 2024 at 07:22, Ekansh Gupta <quic_ekangupt@xxxxxxxxxxx> wrote:


On 12/2/2024 6:18 PM, Dmitry Baryshkov wrote:
On Mon, Dec 02, 2024 at 03:27:43PM +0530, Ekansh Gupta wrote:
On 11/22/2024 12:23 AM, Dmitry Baryshkov wrote:
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@xxxxxxxxxxx>
---
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.
Thanks for your review. The reason of not having single file for all processes is that
I can run 100s of iteration for any process(say calculator) and every time the properties
of the process can differ(like buffer, session etc.). For this reason, I'm creating and
deleting the debugfs files for every process run.

Do you see any advantage of using fdinfo over debugfs? I'm not sure if we can add all
the information(like in debugfs) here.
Which information is actually useful / interesting for application
developers? If not for the fdinfo, I might still vote for a single file
rather than a pile of per-process data.
Let’s say I am trying to do debugfs read when 10+ or more sessions are active per channel, then for pushing data of nth process in a single file, I would have to wait for n-1 processes, by that time process data might get changed. How do you suggest handling this?
I have tried to capture all the information that could be useful.

I can try changes to maintain single file for all active processes. Having this file specific
to a channel should be fine, right? like fastrpc_adsp, fastrpc_cdsp, etc.? Each file will
carry information of all processes using that remoteproc.
I think it's a better idea, yes.

Hi all,

I'm adding Deepika <quic_dsi@xxxxxxxxxxx> to this thread who is reworking
on this patch series.

//Ekansh

--ekansh
--ekansh