-----Original Message-----
From: Al Viro <redacted> On Behalf Of Al Viro
Sent: Wednesday, May 19, 2021 8:49 AM
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Justin He <redacted>; Petr Mladek <pmladek@suse.com>; Steven
Rostedt [off-list ref]; Sergey Senozhatsky
[off-list ref]; Andy Shevchenko
[off-list ref]; Rasmus Villemoes
[off-list ref]; Jonathan Corbet [off-list ref]; Heiko
Carstens [off-list ref]; Vasily Gorbik [off-list ref]; Christian
Borntraeger [off-list ref]; Eric W . Biederman
[off-list ref]; Darrick J. Wong [off-list ref]; Peter
Zijlstra (Intel) [off-list ref]; Ira Weiny [off-list ref];
Eric Biggers [off-list ref]; Ahmed S. Darwish
[off-list ref]; open list:DOCUMENTATION <linux-
doc@vger.kernel.org>; Linux Kernel Mailing List <linux-
kernel@vger.kernel.org>; linux-s390 [off-list ref]; linux-
fsdevel [off-list ref]
Subject: [PATCH 03/14] d_path: regularize handling of root dentry in
__dentry_path()

All path-forming primitives boil down to sequence of prepend_name()
on dentries encountered along the way toward root.  Each time we prepend
/ + dentry name to the buffer.  Normally that does exactly what we want,
but there's a corner case when we don't call prepend_name() at all (in case
of __dentry_path() that happens if we are given root dentry).  We obviously
want to end up with "/", rather than "", so this corner case needs to be
handled.

__dentry_path() used to manually put '/' in the end of buffer before
doing anything else, to be overwritten by the first call of prepend_name()
if one happens and to be left in place if we don't call prepend_name() at
all.  That required manually checking that we had space in the buffer
(prepend_name() and prepend() take care of such checks themselves) and lead
to clumsy keeping track of return value.

A better approach is to check if the main loop has added anything
into the buffer and prepend "/" if it hasn't.  A side benefit of using
prepend()
is that it does the right thing if we'd already run out of buffer, making
the overflow-handling logics simpler.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Reviewed-by: Jia He <redacted>


--
Cheers,
Justin (Jia He)


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