Messages in this thread | | | Date | Sun, 01 Feb 2009 09:37:20 -0600 | From | Eric Sandeen <> | Subject | Re: [xfs-masters] [PATCH] fs: Add new pre-allocation ioctls to vfs for compatibility with legacy xfs ioctls |
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Boaz Harrosh wrote:
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> I don't understand > > if you have a structure like > struct foo { > u32 one; > u32 two; > }; > vs > struct foo_packed { > u32 one; > u32 two; > } __packed; > > Just adding an __attribute__((packed)) to it clearly does not change > the layout of the structure. Are you saying the __attribute__((packed)) > is an hint to the compiler that foo_packed might be used unaligned. This > is just brain-dead, because I can use an unaligned pointer to foo just as > I can to foo_packed. Otherwise there is no difference what-so-ever between > the two. I have to see it to believe. It is totally the wrong hint in the > wrong place taking away valuable meaning of saying "please don't use padding > holes in this structure" > > Sorry for been so slow, I just don't get it. > Boaz
While I'm no gcc guru, I can confirm that gratuitous use of the packed attribute is suboptimal; adding "packed" to every ondisk structure made obdump -d xfs.ko | wc -l explode by about 15,000 lines on ia64.
-Eric
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