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author | Linus Torvalds <torvalds@linux-foundation.org> | 2014-01-25 23:17:34 +0400 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-01-25 23:17:34 +0400 |
commit | 4ba9920e5e9c0e16b5ed24292d45322907bb9035 (patch) | |
tree | 7d023baea59ed0886ded1f0b6d1c6385690b88f7 /Documentation/unaligned-memory-access.txt | |
parent | 82c477669a4665eb4e52030792051e0559ee2a36 (diff) | |
parent | 8b662fe70c68282f78482dc272df0c4f355e49f5 (diff) | |
download | linux-4ba9920e5e9c0e16b5ed24292d45322907bb9035.tar.xz |
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next
Pull networking updates from David Miller:
1) BPF debugger and asm tool by Daniel Borkmann.
2) Speed up create/bind in AF_PACKET, also from Daniel Borkmann.
3) Correct reciprocal_divide and update users, from Hannes Frederic
Sowa and Daniel Borkmann.
4) Currently we only have a "set" operation for the hw timestamp socket
ioctl, add a "get" operation to match. From Ben Hutchings.
5) Add better trace events for debugging driver datapath problems, also
from Ben Hutchings.
6) Implement auto corking in TCP, from Eric Dumazet. Basically, if we
have a small send and a previous packet is already in the qdisc or
device queue, defer until TX completion or we get more data.
7) Allow userspace to manage ipv6 temporary addresses, from Jiri Pirko.
8) Add a qdisc bypass option for AF_PACKET sockets, from Daniel
Borkmann.
9) Share IP header compression code between Bluetooth and IEEE802154
layers, from Jukka Rissanen.
10) Fix ipv6 router reachability probing, from Jiri Benc.
11) Allow packets to be captured on macvtap devices, from Vlad Yasevich.
12) Support tunneling in GRO layer, from Jerry Chu.
13) Allow bonding to be configured fully using netlink, from Scott
Feldman.
14) Allow AF_PACKET users to obtain the VLAN TPID, just like they can
already get the TCI. From Atzm Watanabe.
15) New "Heavy Hitter" qdisc, from Terry Lam.
16) Significantly improve the IPSEC support in pktgen, from Fan Du.
17) Allow ipv4 tunnels to cache routes, just like sockets. From Tom
Herbert.
18) Add Proportional Integral Enhanced packet scheduler, from Vijay
Subramanian.
19) Allow openvswitch to mmap'd netlink, from Thomas Graf.
20) Key TCP metrics blobs also by source address, not just destination
address. From Christoph Paasch.
21) Support 10G in generic phylib. From Andy Fleming.
22) Try to short-circuit GRO flow compares using device provided RX
hash, if provided. From Tom Herbert.
The wireless and netfilter folks have been busy little bees too.
* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next: (2064 commits)
net/cxgb4: Fix referencing freed adapter
ipv6: reallocate addrconf router for ipv6 address when lo device up
fib_frontend: fix possible NULL pointer dereference
rtnetlink: remove IFLA_BOND_SLAVE definition
rtnetlink: remove check for fill_slave_info in rtnl_have_link_slave_info
qlcnic: update version to 5.3.55
qlcnic: Enhance logic to calculate msix vectors.
qlcnic: Refactor interrupt coalescing code for all adapters.
qlcnic: Update poll controller code path
qlcnic: Interrupt code cleanup
qlcnic: Enhance Tx timeout debugging.
qlcnic: Use bool for rx_mac_learn.
bonding: fix u64 division
rtnetlink: add missing IFLA_BOND_AD_INFO_UNSPEC
sfc: Use the correct maximum TX DMA ring size for SFC9100
Add Shradha Shah as the sfc driver maintainer.
net/vxlan: Share RX skb de-marking and checksum checks with ovs
tulip: cleanup by using ARRAY_SIZE()
ip_tunnel: clear IPCB in ip_tunnel_xmit() in case dst_link_failure() is called
net/cxgb4: Don't retrieve stats during recovery
...
Diffstat (limited to 'Documentation/unaligned-memory-access.txt')
-rw-r--r-- | Documentation/unaligned-memory-access.txt | 28 |
1 files changed, 19 insertions, 9 deletions
diff --git a/Documentation/unaligned-memory-access.txt b/Documentation/unaligned-memory-access.txt index f866c72291bf..a445da098bc6 100644 --- a/Documentation/unaligned-memory-access.txt +++ b/Documentation/unaligned-memory-access.txt @@ -137,24 +137,34 @@ Code that causes unaligned access ================================= With the above in mind, let's move onto a real life example of a function -that can cause an unaligned memory access. The following function adapted +that can cause an unaligned memory access. The following function taken from include/linux/etherdevice.h is an optimized routine to compare two ethernet MAC addresses for equality. -unsigned int compare_ether_addr(const u8 *addr1, const u8 *addr2) +bool ether_addr_equal(const u8 *addr1, const u8 *addr2) { - const u16 *a = (const u16 *) addr1; - const u16 *b = (const u16 *) addr2; +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS + u32 fold = ((*(const u32 *)addr1) ^ (*(const u32 *)addr2)) | + ((*(const u16 *)(addr1 + 4)) ^ (*(const u16 *)(addr2 + 4))); + + return fold == 0; +#else + const u16 *a = (const u16 *)addr1; + const u16 *b = (const u16 *)addr2; return ((a[0] ^ b[0]) | (a[1] ^ b[1]) | (a[2] ^ b[2])) != 0; +#endif } -In the above function, the reference to a[0] causes 2 bytes (16 bits) to -be read from memory starting at address addr1. Think about what would happen -if addr1 was an odd address such as 0x10003. (Hint: it'd be an unaligned -access.) +In the above function, when the hardware has efficient unaligned access +capability, there is no issue with this code. But when the hardware isn't +able to access memory on arbitrary boundaries, the reference to a[0] causes +2 bytes (16 bits) to be read from memory starting at address addr1. + +Think about what would happen if addr1 was an odd address such as 0x10003. +(Hint: it'd be an unaligned access.) Despite the potential unaligned access problems with the above function, it -is included in the kernel anyway but is understood to only work on +is included in the kernel anyway but is understood to only work normally on 16-bit-aligned addresses. It is up to the caller to ensure this alignment or not use this function at all. This alignment-unsafe function is still useful as it is a decent optimization for the cases when you can ensure alignment, |