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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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