linux-ext4 - Re: simplify procfs code for seq

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Date:   Wed, 9 May 2018 19:53:31 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-acpi@...r.kernel.org, drbd-dev@...ts.linbit.com,
        linux-ide@...r.kernel.org, netdev@...r.kernel.org,
        linux-rtc@...r.kernel.org, megaraidlinux.pdl@...adcom.com,
        linux-scsi@...r.kernel.org, devel@...verdev.osuosl.org,
        linux-afs@...ts.infradead.org, linux-ext4@...r.kernel.org,
        jfs-discussion@...ts.sourceforge.net,
        netfilter-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: simplify procfs code for seq_file instances V2

On Sun, May 06, 2018 at 06:45:31PM +0100, Al Viro wrote:
> On Sun, May 06, 2018 at 08:19:49PM +0300, Alexey Dobriyan wrote:

> > @@ -62,9 +62,9 @@ struct proc_dir_entry {
> >  	umode_t mode;
> >  	u8 namelen;
> >  #ifdef CONFIG_64BIT
> > -#define SIZEOF_PDE_INLINE_NAME	(192-139)
> > +#define SIZEOF_PDE_INLINE_NAME	(192-155)
> >  #else
> > -#define SIZEOF_PDE_INLINE_NAME	(128-87)
> > +#define SIZEOF_PDE_INLINE_NAME	(128-95)
> 
> >  #endif
> >  	char inline_name[SIZEOF_PDE_INLINE_NAME];
> >  } __randomize_layout;
> 
> *UGH*

I agree. Maintaining these numbers is a pain point.
Who knew people were going to start adding fields right away.

> Both to the original state and that kind of "adjustments".
> Incidentally, with __bugger_layout in there these expressions
> are simply wrong.

Struct randomization is exempt from maintaining sizeof as they are already
screwing cachelines and everything. But if patch works with lockdep and
randomization -- even better.

> If nothing else, I would suggest turning the last one into
> 	char inline_name[];
> in hope that layout won't get... randomized that much and
> used
> 
> #ifdef CONFIG_64BIT
> #define PDE_SIZE 192
> #else
> #define PDE_SIZE 128
> #endif
> 
> union __proc_dir_entry {
> 	char pad[PDE_SIZE];
> 	struct proc_dir_entry real;
> };
> 
> #define SIZEOF_PDE_INLINE_NAME (PDE_SIZE - offsetof(struct proc_dir_entry, inline_name))
> 
> for constants, adjusted sizeof and sizeof_field when creating
> proc_dir_entry_cache and turned proc_root into
> 
> union __proc_dir_entry __proc_root = { .real = {
>         .low_ino        = PROC_ROOT_INO,
>         .namelen        = 5,
>         .mode           = S_IFDIR | S_IRUGO | S_IXUGO,
>         .nlink          = 2,
>         .refcnt         = REFCOUNT_INIT(1),
>         .proc_iops      = &proc_root_inode_operations,
>         .proc_fops      = &proc_root_operations,
>         .parent         = &__proc_root.real,
>         .subdir         = RB_ROOT,
>         .name           = __proc_root.real.inline_name,
>         .inline_name    = "/proc",
> }};
> 
> #define proc_root __proc_root.real
> (or actually used __proc_root.real in all of a 6 places where it remains).
> 
> > -	size_t state_size = PDE(inode)->state_size;
> > +	unsigned int state_size = PDE(inode)->state_size;
> 
> <shakes head>
> You and your "size_t is evil" crusade...

[nods]

        unsigned long           flags;          /* error bits */
        unsigned long           i_state;
        unsigned long           s_blocksize;
        unsigned long           s_flags;
        unsigned long           s_iflags;       /* internal SB_I_* flags */