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SubjectRe: [EXT4 set 7][PATCH 1/1]Remove 32000 subdirs limit.
On Fri, 13 Jul 2007 16:00:48 +0530 Kalpak Shah <kalpak@clusterfs.com> wrote:

> > >
> > > - if (inode->i_nlink >= EXT4_LINK_MAX)
> > > + if (EXT4_DIR_LINK_MAX(inode))
> > > return -EMLINK;
> >
> > argh. WHY_IS_EXT4_FULL_OF_UPPER_CASE_MACROS_WHICH_COULD_BE_IMPLEMENTED
> > as_lower_case_inlines? Sigh. It's all the old-timers, I guess.
> >
> > EXT4_DIR_LINK_MAX() is buggy: it evaluates its arg twice.
>
> #define EXT4_DIR_LINK_MAX(dir) (!is_dx(dir) && (dir)->i_nlink >= EXT4_LINK_MAX)
>
> This just checks if directory has hash indexing in which case we need not worry about EXT4_LINK_MAX subdir limit. If directory is not hash indexed then we will need to enforce a max subdir limit.
>
> Sorry, I didn't understand what is the problem with this macro?

Macros should never evaluate their argument more than once, because if they
do they will misbehave when someone passes them an
expression-with-side-effects:

struct inode *p = q;

EXT4_DIR_LINK_MAX(p++);

one expects `p' to have the value q+1 here. But it might be q+2.

and

EXT4_DIR_LINK_MAX(some_function());

might cause some_function() to be called twice.


This is one of the many problems which gets fixed when we write code in C
rather than in cpp.
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