Patchwork [07/18] iov: add iov_discard_front/back() to remove data

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Submitter Stefan Hajnoczi
Date Jan. 2, 2013, 3:15 p.m.
Message ID <1357139756-11951-8-git-send-email-stefanha@redhat.com>
Download mbox | patch
Permalink /patch/209071/
State New
Headers show

Comments

Stefan Hajnoczi - Jan. 2, 2013, 3:15 p.m.
The iov_discard_front/back() functions remove data from the front or
back of the vector.  This is useful when peeling off header/footer
structs.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/qemu/iov.h | 13 +++++++++++++
 iov.c              | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 64 insertions(+)

Patch

diff --git a/include/qemu/iov.h b/include/qemu/iov.h
index d06f8b9..68d25f2 100644
--- a/include/qemu/iov.h
+++ b/include/qemu/iov.h
@@ -99,4 +99,17 @@  unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
                  const struct iovec *iov, unsigned int iov_cnt,
                  size_t offset, size_t bytes);
 
+/*
+ * Remove a given number of bytes from the front or back of a vector.
+ * This may update iov and/or iov_cnt to exclude iovec elements that are
+ * no longer required.
+ *
+ * The number of bytes actually discarded is returned.  This number may be
+ * smaller than requested if the vector is too small.
+ */
+size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
+                         size_t bytes);
+size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
+                        size_t bytes);
+
 #endif
diff --git a/iov.c b/iov.c
index 419e419..92ad77b 100644
--- a/iov.c
+++ b/iov.c
@@ -354,3 +354,54 @@  size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
 {
     return iov_memset(qiov->iov, qiov->niov, offset, fillc, bytes);
 }
+
+size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
+                         size_t bytes)
+{
+    size_t total = 0;
+    struct iovec *cur;
+
+    for (cur = *iov; *iov_cnt > 0; cur++) {
+        if (cur->iov_len > bytes) {
+            cur->iov_base += bytes;
+            cur->iov_len -= bytes;
+            total += bytes;
+            break;
+        }
+
+        bytes -= cur->iov_len;
+        total += cur->iov_len;
+        *iov_cnt -= 1;
+    }
+
+    *iov = cur;
+    return total;
+}
+
+size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
+                        size_t bytes)
+{
+    size_t total = 0;
+    struct iovec *cur;
+
+    if (*iov_cnt == 0) {
+        return 0;
+    }
+
+    cur = iov + (*iov_cnt - 1);
+
+    while (*iov_cnt > 0) {
+        if (cur->iov_len > bytes) {
+            cur->iov_len -= bytes;
+            total += bytes;
+            break;
+        }
+
+        bytes -= cur->iov_len;
+        total += cur->iov_len;
+        cur--;
+        *iov_cnt -= 1;
+    }
+
+    return total;
+}