On Mon, Jun 09 2014, Krzysztof Opasiak wrote:
> As this is an example which will be copy-paste by many users maybe you
> should you struct usb_functionfs_descs_head and struct
> usb_functionfs_descs_head_v2 instead of direct operations using
> hard-coded offsets to make this function more readable?
v3 uses usb_functionfs_descs_head{_v2,} instead of hard-coded offsets.
I also started wondering if it would make sense to go one step further
and define a temporary structure holding the headers. Something like:
----------- >8 ---------------------------------------------------------
/* Read v2 header */
{
const struct {
const struct usb_functionfs_descs_head_v2 header;
const __le32 counts[];
} __attribute__((packed)) *const in = descriptors;
const __le32 *counts = in->counts;
__u32 flags;
if (le32_to_cpu(in->header.magic) !=
FUNCTIONFS_DESCRIPTORS_MAGIC_V2)
return 0;
length = le32_to_cpu(in->header.length);
if (length <= sizeof in->header)
return 0;
length -= sizeof in->header;
flags = le32_to_cpu(in->header.flags);
if (flags & ~(FUNCTIONFS_HAS_FS_DESC | FUNCTIONFS_HAS_HS_DESC |
FUNCTIONFS_HAS_SS_DESC))
return 0;
#define GET_NEXT_COUNT_IF_FLAG(ret, flg) do { \
if (!(flags & (flg))) \
break; \
if (length < 4) \
return 0; \
ret = le32_to_cpu(*counts); \
length -= 4; \
++counts; \
} while (0)
GET_NEXT_COUNT_IF_FLAG(fs_count, FUNCTIONFS_HAS_FS_DESC);
GET_NEXT_COUNT_IF_FLAG(hs_count, FUNCTIONFS_HAS_HS_DESC);
GET_NEXT_COUNT_IF_FLAG(count, FUNCTIONFS_HAS_SS_DESC);
count = fs_count + hs_count;
if (!count)
return 0;
descs_start = descs_end = (const void *)counts;
#undef GET_NEXT_COUNT_IF_FLAG
}
----------- >8 ---------------------------------------------------------
/* Allocate legacy descriptors and copy the data. */
{
struct {
struct usb_functionfs_descs_head header;
__u8 descriptors[];
} __attribute__((packed)) *out;
length = sizeof out->header + (descs_end - descs_start);
out = malloc(length);
out->header.magic = cpu_to_le32(FUNCTIONFS_DESCRIPTORS_MAGIC);
out->header.length = cpu_to_le32(length);
out->header.fs_count = cpu_to_le32(fs_count);
out->header.hs_count = cpu_to_le32(hs_count);
memcpy(out->descriptors, descs_start, descs_end - descs_start);
*legacy = out;
}
----------- >8 ---------------------------------------------------------
Thoughts?
--
Best regards, _ _
.o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michał “mina86” Nazarewicz (o o)
ooo +--<m...@google.com>--<xmpp:min...@jabber.org>--ooO--(_)--Ooo--
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