skbuff.h: Improve the checksum related comments

Fixed the punctuation and some typos.
Improved some sentences with minor changes.

No change of semantics or code.

Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/skbuff.h

@@ -47,8 +47,8 @@
  * A. IP checksum related features
  *
  * Drivers advertise checksum offload capabilities in the features of a device.
- * From the stack's point of view these are capabilities offered by the driver,
- * a driver typically only advertises features that it is capable of offloading
+ * From the stack's point of view these are capabilities offered by the driver.
+ * A driver typically only advertises features that it is capable of offloading
  * to its device.
  *
  * The checksum related features are:
@@ -63,7 +63,7 @@
  *			  TCP or UDP packets over IPv4. These are specifically
  *			  unencapsulated packets of the form IPv4|TCP or
  *			  IPv4|UDP where the Protocol field in the IPv4 header
- *			  is TCP or UDP. The IPv4 header may contain IP options
+ *			  is TCP or UDP. The IPv4 header may contain IP options.
  *			  This feature cannot be set in features for a device
  *			  with NETIF_F_HW_CSUM also set. This feature is being
  *			  DEPRECATED (see below).
@@ -79,13 +79,13 @@
  *			  DEPRECATED (see below).
  *
  *	NETIF_F_RXCSUM - Driver (device) performs receive checksum offload.
- *			 This flag is used only used to disable the RX checksum
+ *			 This flag is only used to disable the RX checksum
  *			 feature for a device. The stack will accept receive
  *			 checksum indication in packets received on a device
  *			 regardless of whether NETIF_F_RXCSUM is set.
  *
  * B. Checksumming of received packets by device. Indication of checksum
- *    verification is in set skb->ip_summed. Possible values are:
+ *    verification is set in skb->ip_summed. Possible values are:
  *
  * CHECKSUM_NONE:
  *
@@ -115,16 +115,16 @@
  *   the packet minus one that have been verified as CHECKSUM_UNNECESSARY.
  *   For instance if a device receives an IPv6->UDP->GRE->IPv4->TCP packet
  *   and a device is able to verify the checksums for UDP (possibly zero),
- *   GRE (checksum flag is set), and TCP-- skb->csum_level would be set to
+ *   GRE (checksum flag is set) and TCP, skb->csum_level would be set to
  *   two. If the device were only able to verify the UDP checksum and not
- *   GRE, either because it doesn't support GRE checksum of because GRE
+ *   GRE, either because it doesn't support GRE checksum or because GRE
  *   checksum is bad, skb->csum_level would be set to zero (TCP checksum is
  *   not considered in this case).
  *
  * CHECKSUM_COMPLETE:
  *
  *   This is the most generic way. The device supplied checksum of the _whole_
- *   packet as seen by netif_rx() and fills out in skb->csum. Meaning, the
+ *   packet as seen by netif_rx() and fills in skb->csum. This means the
  *   hardware doesn't need to parse L3/L4 headers to implement this.
  *
  *   Notes:
@@ -153,8 +153,8 @@
  *   from skb->csum_start up to the end, and to record/write the checksum at
  *   offset skb->csum_start + skb->csum_offset. A driver may verify that the
  *   csum_start and csum_offset values are valid values given the length and
- *   offset of the packet, however they should not attempt to validate that the
- *   checksum refers to a legitimate transport layer checksum-- it is the
+ *   offset of the packet, but it should not attempt to validate that the
+ *   checksum refers to a legitimate transport layer checksum -- it is the
  *   purview of the stack to validate that csum_start and csum_offset are set
  *   correctly.
  *
@@ -178,18 +178,18 @@
  *
  * CHECKSUM_UNNECESSARY:
  *
- *   This has the same meaning on as CHECKSUM_NONE for checksum offload on
+ *   This has the same meaning as CHECKSUM_NONE for checksum offload on
  *   output.
  *
  * CHECKSUM_COMPLETE:
  *   Not used in checksum output. If a driver observes a packet with this value
- *   set in skbuff, if should treat as CHECKSUM_NONE being set.
+ *   set in skbuff, it should treat the packet as if CHECKSUM_NONE were set.
  *
  * D. Non-IP checksum (CRC) offloads
  *
  *   NETIF_F_SCTP_CRC - This feature indicates that a device is capable of
  *     offloading the SCTP CRC in a packet. To perform this offload the stack
- *     will set set csum_start and csum_offset accordingly, set ip_summed to
+ *     will set csum_start and csum_offset accordingly, set ip_summed to
  *     CHECKSUM_PARTIAL and set csum_not_inet to 1, to provide an indication in
  *     the skbuff that the CHECKSUM_PARTIAL refers to CRC32c.
  *     A driver that supports both IP checksum offload and SCTP CRC32c offload
@@ -200,20 +200,20 @@
  *   NETIF_F_FCOE_CRC - This feature indicates that a device is capable of
  *     offloading the FCOE CRC in a packet. To perform this offload the stack
  *     will set ip_summed to CHECKSUM_PARTIAL and set csum_start and csum_offset
- *     accordingly. Note the there is no indication in the skbuff that the
- *     CHECKSUM_PARTIAL refers to an FCOE checksum, a driver that supports
+ *     accordingly. Note that there is no indication in the skbuff that the
+ *     CHECKSUM_PARTIAL refers to an FCOE checksum, so a driver that supports
  *     both IP checksum offload and FCOE CRC offload must verify which offload
- *     is configured for a packet presumably by inspecting packet headers.
+ *     is configured for a packet, presumably by inspecting packet headers.
  *
  * E. Checksumming on output with GSO.
  *
  * In the case of a GSO packet (skb_is_gso(skb) is true), checksum offload
  * is implied by the SKB_GSO_* flags in gso_type. Most obviously, if the
  * gso_type is SKB_GSO_TCPV4 or SKB_GSO_TCPV6, TCP checksum offload as
  * part of the GSO operation is implied. If a checksum is being offloaded
- * with GSO then ip_summed is CHECKSUM_PARTIAL, csum_start and csum_offset
- * are set to refer to the outermost checksum being offload (two offloaded
- * checksums are possible with UDP encapsulation).
+ * with GSO then ip_summed is CHECKSUM_PARTIAL, and both csum_start and
+ * csum_offset are set to refer to the outermost checksum being offloaded
+ * (two offloaded checksums are possible with UDP encapsulation).
  */
 
 /* Don't change this without changing skb_csum_unnecessary! */