linux-ext4 - Re: [PATCH][RFC] make take_dentry_name

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Message-ID: <20241210024523.GD3387508@ZenIV>
Date: Tue, 10 Dec 2024 02:45:23 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH][RFC] make take_dentry_name_snapshot() lockless

On Mon, Dec 09, 2024 at 11:12:37PM +0000, Al Viro wrote:
> 
> Actually, grepping for DNAME_INLINE_LEN brings some interesting hits:
> drivers/net/ieee802154/adf7242.c:1165:  char debugfs_dir_name[DNAME_INLINE_LEN + 1];
> 	cargo-culted, AFAICS; would be better off with a constant of their own.
> 
> fs/ext4/fast_commit.c:326:              fc_dentry->fcd_name.len > DNAME_INLINE_LEN)
> fs/ext4/fast_commit.c:452:      if (dentry->d_name.len > DNAME_INLINE_LEN) {
> fs/ext4/fast_commit.c:1332:                     fc_dentry->fcd_name.len > DNAME_INLINE_LEN)
> fs/ext4/fast_commit.h:113:      unsigned char fcd_iname[DNAME_INLINE_LEN];      /* Dirent name string */
> 	Looks like that might want struct name_snapshot, along with
> {take,release}_dentry_name_snapshot().

See viro/vfs.git#work.dcache.  I've thrown ext4/fast_commit conversion
into the end of that pile.  NOTE: that stuff obviously needs profiling.
It does survive light testing (boot/ltp/xfstests), but review and more
testing (including serious profiling) is obviously needed.

Patches in followups...