Re: [PATCH v2] b43: don't save dentries for debugfs

On Wed, May 19, 2021 at 08:57:00AM -0700, Jeff Johnson wrote:

On 2021-05-19 08:42, Greg Kroah-Hartman wrote:

quoted

On Wed, May 19, 2021 at 08:04:59AM -0700, Jeff Johnson wrote:

quoted

On 2021-05-18 22:05, Greg Kroah-Hartman wrote:

quoted

On Tue, May 18, 2021 at 03:00:44PM -0700, Jeff Johnson wrote:

quoted

On 2021-05-18 12:29, Jeff Johnson wrote:
Would still like guidance on if there is a recommended way to get a
dentry not associated with debugfs.

What do you exactly mean by "not associated with debugfs"?

And why are you passing a debugfs dentry to relay_open()?  That feels
really wrong and fragile.

I don't know the history but the relay documentation tells us:
"If you want a directory structure to contain your relay files,
you should create it using the host filesystem’s directory
creation function, e.g. debugfs_create_dir()..."

So my guess is that the original implementation followed that
advice.  I see 5 clients of this functionality, and all 5 pass a
dentry returned from debugfs_create_dir():

drivers/gpu/drm/i915/gt/uc/intel_guc_log.c, line 384
drivers/net/wireless/ath/ath10k/spectral.c, line 534
drivers/net/wireless/ath/ath11k/spectral.c, line 902
drivers/net/wireless/ath/ath9k/common-spectral.c, line 1077
kernel/trace/blktrace.c, line 549

Ah, that's just the "parent" dentry for the relayfs file.  That's fine,
not a big deal, debugfs will always provide a way for you to get that if
needed.

Unless debugfs is disabled, like on Android, which is the real problem I'm
trying to solve.

Then use some other filesystem to place your relay file in.  A relay
file is not a file that userspace should rely on for normal operation,
so why do you need it at all?

What tools/operation requires access to this file that systems without
debugfs support is causing problems on?

thanks,

greg k-h