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SubjectRe: [PATCH][RFC] %pd - for printing dentry name
On Tue, Feb 02, 2010 at 06:32:31AM -0700, Matthew Wilcox wrote:
> How about doing this:
>
> struct qstr {
> - const unsigned char *name;
> + const unsigned char name[0];
> }
>
> struct dentry {
> - struct qstr d_name;
> + struct qstr *d_name;
> - unsigned char d_iname[DNAME_INLINE_LEN_MIN]; /* small names */
> + union {
> + struct qstr d_iname;
> + char pad[DNAME_INLINE_LEN_MIN];
> + };
> }
>
> Doesn't increase the size of struct dentry, and puts the hash and len
> with the name. Increases long name allocations by 8 bytes each.
>
> I think reusing the d_iname is OK. As long as we always limit the
> number of characters printed to the 'len' element, we should never get
> an overrun. At worst, we get a mixture of the previous name and the
> next name ... and that's a significant canary in itself.

You are creating an extra deref in normal case. Inline names are common.
Putting len and hash with the name probably not a win - most of the time
you don't look at actual characters and rely on mismatches in other
components to skip the candidate during search.


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