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util/iov: add iov_discard_undo()

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The iov_discard_front/back() operations are useful for parsing iovecs
but they modify the array elements. If the original array is needed
after parsing finishes there is currently no way to restore it.

Although g_memdup() can be used before performing destructive
iov_discard_front/back() operations, this is inefficient.

Introduce iov_discard_undo() to restore the array to the state prior to
an iov_discard_front/back() operation.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Li Qiang <liq3ea@gmail.com>
Message-Id: <20200917094455.822379-2-stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi
2020-09-17 10:44:53 +01:00
parent bd0bbb9aba
commit 9dd6f7c28e
3 changed files with 234 additions and 4 deletions
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50
util/iov.c
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@ -636,14 +636,33 @@ void qemu_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src, void *buf)
}
}
size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
size_t bytes)
void iov_discard_undo(IOVDiscardUndo *undo)
{
/* Restore original iovec if it was modified */
if (undo->modified_iov) {
*undo->modified_iov = undo->orig;
}
}
size_t iov_discard_front_undoable(struct iovec **iov,
unsigned int *iov_cnt,
size_t bytes,
IOVDiscardUndo *undo)
{
size_t total = 0;
struct iovec *cur;
if (undo) {
undo->modified_iov = NULL;
}
for (cur = *iov; *iov_cnt > 0; cur++) {
if (cur->iov_len > bytes) {
if (undo) {
undo->modified_iov = cur;
undo->orig = *cur;
}
cur->iov_base += bytes;
cur->iov_len -= bytes;
total += bytes;
@ -659,12 +678,24 @@ size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
return total;
}
size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
size_t bytes)
size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
size_t bytes)
{
return iov_discard_front_undoable(iov, iov_cnt, bytes, NULL);
}
size_t iov_discard_back_undoable(struct iovec *iov,
unsigned int *iov_cnt,
size_t bytes,
IOVDiscardUndo *undo)
{
size_t total = 0;
struct iovec *cur;
if (undo) {
undo->modified_iov = NULL;
}
if (*iov_cnt == 0) {
return 0;
}
@ -673,6 +704,11 @@ size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
while (*iov_cnt > 0) {
if (cur->iov_len > bytes) {
if (undo) {
undo->modified_iov = cur;
undo->orig = *cur;
}
cur->iov_len -= bytes;
total += bytes;
break;
@ -687,6 +723,12 @@ size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
return total;
}
size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
size_t bytes)
{
return iov_discard_back_undoable(iov, iov_cnt, bytes, NULL);
}
void qemu_iovec_discard_back(QEMUIOVector *qiov, size_t bytes)
{
size_t total;