Julia Lawall <julia.lawall@xxxxxxx> writes: > On Sat, 6 Oct 2018, Kalle Valo wrote: > >> Julia Lawall <julia.lawall@xxxxxxx> writes: >> >> > On Fri, 5 Oct 2018, Kalle Valo wrote: >> > >> >> YueHaibing <yuehaibing@xxxxxxxxxx> writes: >> >> >> >> > Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE >> >> > for debugfs files. >> >> > >> >> > Semantic patch information: >> >> > Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file() >> >> > imposes some significant overhead as compared to >> >> > DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe(). >> >> > >> >> > Generated by: scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci >> >> >> >> Just out of curiosity, what kind of overhead are we talking about here? >> > >> > The log message on the commit introducing the semantic patch says the >> > following: >> > >> > In order to protect against file removal races, debugfs files created via >> > debugfs_create_file() now get wrapped by a struct file_operations at their >> > opening. >> > >> > If the original struct file_operations are known to be safe against removal >> > races by themselves already, the proxy creation may be bypassed by creating >> > the files through debugfs_create_file_unsafe(). >> > >> > In order to help debugfs users who use the common >> > DEFINE_SIMPLE_ATTRIBUTE() + debugfs_create_file() >> > idiom to transition to removal safe struct file_operations, the helper >> > macro DEFINE_DEBUGFS_ATTRIBUTE() has been introduced. >> > >> > Thus, the preferred strategy is to use >> > DEFINE_DEBUGFS_ATTRIBUTE() + debugfs_create_file_unsafe() >> > now. >> >> I admit that I didn't have time to investigate this is detail but I'm >> still not understanding where is that "significant overhead" coming from >> and how big of overhead are we talking about? I guess it has something >> to do with full_proxy_open() vs open_proxy_open()? >> >> Not that I'm against this patch, just curious when I see someone >> claiming "significant overhead" which is not obvious for me. > > The message with the semantic patch doesn't really talk about significant > overhead. Maybe YueHaibing can discuss with the person who proposed the > semantic patch what the actual issue is, and when the proposed change is > actually applicable. Actually commit 5103068eaca2 mentions "significant overhead": --- /dev/null +++ b/scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci @@ -0,0 +1,67 @@ +/// Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE +/// for debugfs files. +/// +//# Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file() +//# imposes some significant overhead as compared to +//# DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe(). But I'll anyway apply this patch as I don't see anything wrong with it. I was just trying to learn where this overhead is :) -- Kalle Valo
