On Mon, 2005-01-31 at 16:20 +0530, cranium 2003 wrote:
> Hello,
> In linux kernel source etheernet header is defined as structure as
> struct ethhdr
> {
> unsigned char h_dest[ETH_ALEN]; /* destination eth addr */
> unsigned char h_source[ETH_ALEN]; /* source ether addr */
> unsigned short h_proto; /* packet type ID field */
> } __attribute__((packed));
> I want to know what __attribute__((packed)) meance?
> It is not looking as a structure object then what is thati?
Your ethernet header is 14 bytes long so the "packed" attribute
tells the compiler to to pack the structure to 14 bytes and not
try to byte align it on a word boundary (as it would do without
specifying this keyword).
from "info gcc"
`packed'
The `packed' attribute specifies that a variable or structure field
should have the smallest possible alignment--one byte for a
variable, and one bit for a field, unless you specify a larger
value with the `aligned' attribute.
Here is a structure in which the field `x' is packed, so that it
immediately follows `a':
struct foo
{
char a;
int x[2] __attribute__ ((packed));
};
HTH,
-mandeep
> regards,
> cranium
>
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> Kernelnewbies: Help each other learn about the Linux kernel.
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>
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