RE: [PATCH 03/14] d_path: regularize handling of root dentry in __dentry_path()

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> -----Original Message-----
> From: Al Viro <viro@xxxxxxxxxxxxxxxx> On Behalf Of Al Viro
> Sent: Wednesday, May 19, 2021 8:49 AM
> To: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Justin He <Justin.He@xxxxxxx>; Petr Mladek <pmladek@xxxxxxxx>; Steven
> Rostedt <rostedt@xxxxxxxxxxx>; Sergey Senozhatsky
> <senozhatsky@xxxxxxxxxxxx>; Andy Shevchenko
> <andriy.shevchenko@xxxxxxxxxxxxxxx>; Rasmus Villemoes
> <linux@xxxxxxxxxxxxxxxxxx>; Jonathan Corbet <corbet@xxxxxxx>; Heiko
> Carstens <hca@xxxxxxxxxxxxx>; Vasily Gorbik <gor@xxxxxxxxxxxxx>; Christian
> Borntraeger <borntraeger@xxxxxxxxxx>; Eric W . Biederman
> <ebiederm@xxxxxxxxxxxx>; Darrick J. Wong <darrick.wong@xxxxxxxxxx>; Peter
> Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>; Ira Weiny <ira.weiny@xxxxxxxxx>;
> Eric Biggers <ebiggers@xxxxxxxxxx>; Ahmed S. Darwish
> <a.darwish@xxxxxxxxxxxxx>; open list:DOCUMENTATION <linux-
> doc@xxxxxxxxxxxxxxx>; Linux Kernel Mailing List <linux-
> kernel@xxxxxxxxxxxxxxx>; linux-s390 <linux-s390@xxxxxxxxxxxxxxx>; linux-
> fsdevel <linux-fsdevel@xxxxxxxxxxxxxxx>
> 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@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Jia He <justin.he@xxxxxxx>


--
Cheers,
Justin (Jia He)


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