Messages in this thread | | | Date | Fri, 13 Jul 2007 09:53:43 -0700 | From | Andrew Morton <> | Subject | Re: [EXT4 set 7][PATCH 1/1]Remove 32000 subdirs limit. |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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