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Re: [Qemu-devel] [PATCHv4 02/11] change iov_* function prototypes to be


From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCHv4 02/11] change iov_* function prototypes to be more appropriate
Date: Fri, 16 Mar 2012 11:14:56 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.2) Gecko/20120216 Thunderbird/10.0.2

On 03/15/2012 04:00 PM, Michael Tokarev wrote:
Reorder arguments to be more natural, readable and
consistent with other iov_* functions, and change
argument names, from:
  iov_from_buf(iov, iov_cnt, buf, iov_off, size)
to
  iov_from_buf(iov, iov_cnt, offset, buf, bytes)

The result becomes natural English:

I don't think this is a good idea. This is code churn for nothing but cosmetic reasons. I don't think there's a lot of value in that.


  copy data to this `iov' vector with `iov_cnt'
  elements starting at byte offset `offset'
  from memory buffer `buf', processing `bytes'
  bytes max.

(Try to read the original prototype this way).

Also change iov_clear() to more general iov_memset()
(it uses memset() internally anyway).

While at it, add comments to the header file
describing what the routines actually does.

The patch only renames argumens in the header, but
keeps old names in the implementation.  The next
patch will touch actual code to match.

Now, it might look wrong to pay so much attention
to so small things.  But we've so many badly designed
interfaces already so the whole thing becomes rather
confusing or error prone.  One example of this is
previous commit and small discussion which emerged
from it, with an outcome that the utility functions
like these aren't well-understdandable, leading to
strange usage cases.  That's why I paid quite some
attention to this set of functions and a few
others in subsequent patches.

Signed-off-by: Michael Tokarev<address@hidden>
---
  hw/rtl8139.c           |    2 +-
  hw/usb/core.c          |    6 +++---
  hw/virtio-balloon.c    |    4 ++--
  hw/virtio-net.c        |    4 ++--
  hw/virtio-serial-bus.c |    6 +++---
  iov.c                  |   14 +++++++-------
  iov.h                  |   42 +++++++++++++++++++++++++++++++++++++-----
  net.c                  |    2 +-
  8 files changed, 56 insertions(+), 24 deletions(-)

diff --git a/hw/rtl8139.c b/hw/rtl8139.c
index 05b8e1e..e837079 100644
--- a/hw/rtl8139.c
+++ b/hw/rtl8139.c
@@ -1799,7 +1799,7 @@ static void rtl8139_transfer_frame(RTL8139State *s, 
uint8_t *buf, int size,
          if (iov) {
              buf2_size = iov_size(iov, 3);
              buf2 = g_malloc(buf2_size);
-            iov_to_buf(iov, 3, buf2, 0, buf2_size);
+            iov_to_buf(iov, 3, 0, buf2, buf2_size);
              buf = buf2;
          }

diff --git a/hw/usb/core.c b/hw/usb/core.c
index a4048fe..4a213aa 100644
--- a/hw/usb/core.c
+++ b/hw/usb/core.c
@@ -516,10 +516,10 @@ void usb_packet_copy(USBPacket *p, void *ptr, size_t 
bytes)
      switch (p->pid) {
      case USB_TOKEN_SETUP:
      case USB_TOKEN_OUT:
-        iov_to_buf(p->iov.iov, p->iov.niov, ptr, p->result, bytes);
+        iov_to_buf(p->iov.iov, p->iov.niov, p->result, ptr, bytes);
          break;
      case USB_TOKEN_IN:
-        iov_from_buf(p->iov.iov, p->iov.niov, ptr, p->result, bytes);
+        iov_from_buf(p->iov.iov, p->iov.niov, p->result, ptr, bytes);
          break;
      default:
          fprintf(stderr, "%s: invalid pid: %x\n", __func__, p->pid);
@@ -533,7 +533,7 @@ void usb_packet_skip(USBPacket *p, size_t bytes)
      assert(p->result>= 0);
      assert(p->result + bytes<= p->iov.size);
      if (p->pid == USB_TOKEN_IN) {
-        iov_clear(p->iov.iov, p->iov.niov, p->result, bytes);
+        iov_memset(p->iov.iov, p->iov.niov, p->result, 0, bytes);
      }
      p->result += bytes;
  }
diff --git a/hw/virtio-balloon.c b/hw/virtio-balloon.c
index ce9d2c9..8f0cf33 100644
--- a/hw/virtio-balloon.c
+++ b/hw/virtio-balloon.c
@@ -77,7 +77,7 @@ static void virtio_balloon_handle_output(VirtIODevice *vdev, 
VirtQueue *vq)
          size_t offset = 0;
          uint32_t pfn;

-        while (iov_to_buf(elem.out_sg, elem.out_num,&pfn, offset, 4) == 4) {
+        while (iov_to_buf(elem.out_sg, elem.out_num, offset,&pfn, 4) == 4) {
              ram_addr_t pa;
              ram_addr_t addr;

@@ -118,7 +118,7 @@ static void virtio_balloon_receive_stats(VirtIODevice 
*vdev, VirtQueue *vq)
       */
      reset_stats(s);

-    while (iov_to_buf(elem->out_sg, elem->out_num,&stat, offset, sizeof(stat))
+    while (iov_to_buf(elem->out_sg, elem->out_num, offset,&stat, sizeof(stat))
             == sizeof(stat)) {
          uint16_t tag = tswap16(stat.tag);
          uint64_t val = tswap64(stat.val);
diff --git a/hw/virtio-net.c b/hw/virtio-net.c
index bc5e3a8..65a516f 100644
--- a/hw/virtio-net.c
+++ b/hw/virtio-net.c
@@ -656,8 +656,8 @@ static ssize_t virtio_net_receive(VLANClientState *nc, 
const uint8_t *buf, size_
          }

          /* copy in packet.  ugh */
-        len = iov_from_buf(sg, elem.in_num,
-                           buf + offset, 0, size - offset);
+        len = iov_from_buf(sg, elem.in_num, 0,
+                           buf + offset, size - offset);
          total += len;
          offset += len;
          /* If buffers can't be merged, at this point we
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index abe48ec..41a62d1 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -106,8 +106,8 @@ static size_t write_to_port(VirtIOSerialPort *port,
              break;
          }

-        len = iov_from_buf(elem.in_sg, elem.in_num,
-                           buf + offset, 0, size - offset);
+        len = iov_from_buf(elem.in_sg, elem.in_num, 0,
+                           buf + offset, size - offset);
          offset += len;

          virtqueue_push(vq,&elem, len);
@@ -467,7 +467,7 @@ static void control_out(VirtIODevice *vdev, VirtQueue *vq)
              buf = g_malloc(cur_len);
              len = cur_len;
          }
-        iov_to_buf(elem.out_sg, elem.out_num, buf, 0, cur_len);
+        iov_to_buf(elem.out_sg, elem.out_num, 0, buf, cur_len);

          handle_control_message(vser, buf, cur_len);
          virtqueue_push(vq,&elem, 0);
diff --git a/iov.c b/iov.c
index 0f96493..bc58cab 100644
--- a/iov.c
+++ b/iov.c
@@ -17,8 +17,8 @@

  #include "iov.h"

-size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt,
-                    const void *buf, size_t iov_off, size_t size)
+size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt, size_t iov_off,
+                    const void *buf, size_t size)
  {
      size_t iovec_off, buf_off;
      unsigned int i;
@@ -40,8 +40,8 @@ size_t iov_from_buf(struct iovec *iov, unsigned int iov_cnt,
      return buf_off;
  }

-size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
-                  void *buf, size_t iov_off, size_t size)
+size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt, size_t 
iov_off,
+                  void *buf, size_t size)
  {
      uint8_t *ptr;
      size_t iovec_off, buf_off;
@@ -65,8 +65,8 @@ size_t iov_to_buf(const struct iovec *iov, const unsigned int 
iov_cnt,
      return buf_off;
  }

-size_t iov_clear(const struct iovec *iov, const unsigned int iov_cnt,
-                 size_t iov_off, size_t size)
+size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
+                 size_t iov_off, int fillc, size_t size)
  {
      size_t iovec_off, buf_off;
      unsigned int i;
@@ -77,7 +77,7 @@ size_t iov_clear(const struct iovec *iov, const unsigned int 
iov_cnt,
          if (iov_off<  (iovec_off + iov[i].iov_len)) {
              size_t len = MIN((iovec_off + iov[i].iov_len) - iov_off , size);

-            memset(iov[i].iov_base + (iov_off - iovec_off), 0, len);
+            memset(iov[i].iov_base + (iov_off - iovec_off), fillc, len);

              buf_off += len;
              iov_off += len;
diff --git a/iov.h b/iov.h
index 94d2f78..0b4acf4 100644
--- a/iov.h
+++ b/iov.h
@@ -12,12 +12,44 @@

  #include "qemu-common.h"

+/**
+ * count and return data size, in bytes, of an iovec
+ * starting at `iov' of `iov_cnt' number of elements.
+ */
+size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt);
+
+/**
+ * Copy from single continuous buffer to scatter-gather vector of buffers
+ * (iovec) and back like memcpy() between two continuous memory regions.
+ * Data in single continuous buffer starting at address `buf' and
+ * `bytes' bytes long will be copied to/from an iovec `iov' with
+ * `iov_cnt' number of elements, starting at byte position `offset'
+ * within the iovec.  If the iovec does not contain enough space,
+ * only part of data will be copied, up to the end of the iovec.
+ * Number of bytes actually copied will be returned, which is
+ *  min(bytes, iov_size(iov)-offset)
+ */

But if you're adding documentation (especially to ever function: hint) then I'd be willing to take the above change as a compromise.

However, this should be in gtk-doc format.

Regards,

Anthony Liguori



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