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util/iov: add iov_discard_undo() 

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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23
include/qemu/iov.h
View File

@ -130,6 +130,29 @@ size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
size_t bytes);
/* Information needed to undo an iov_discard_*() operation */
typedef struct {
struct iovec *modified_iov;
struct iovec orig;
} IOVDiscardUndo;
/*
* Undo an iov_discard_front_undoable() or iov_discard_back_undoable()
* operation. If multiple operations are made then each one needs a separate
* IOVDiscardUndo and iov_discard_undo() must be called in the reverse order
* that the operations were made.
*/
void iov_discard_undo(IOVDiscardUndo *undo);
/*
* Undoable versions of iov_discard_front() and iov_discard_back(). Use
* iov_discard_undo() to reset to the state before the discard operations.
*/
size_t iov_discard_front_undoable(struct iovec **iov, unsigned int *iov_cnt,
size_t bytes, IOVDiscardUndo *undo);
size_t iov_discard_back_undoable(struct iovec *iov, unsigned int *iov_cnt,
size_t bytes, IOVDiscardUndo *undo);
typedef struct QEMUIOVector {
struct iovec *iov;
int niov;

165
tests/test-iov.c
View File

@ -26,6 +26,12 @@ static void iov_free(struct iovec *iov, unsigned niov)
g_free(iov);
}
static bool iov_equals(const struct iovec *a, const struct iovec *b,
unsigned niov)
{
return memcmp(a, b, sizeof(a[0]) * niov) == 0;
}
static void test_iov_bytes(struct iovec *iov, unsigned niov,
size_t offset, size_t bytes)
{
@ -335,6 +341,87 @@ static void test_discard_front(void)
iov_free(iov, iov_cnt);
}
static void test_discard_front_undo(void)
{
IOVDiscardUndo undo;
struct iovec *iov;
struct iovec *iov_tmp;
struct iovec *iov_orig;
unsigned int iov_cnt;
unsigned int iov_cnt_tmp;
size_t size;
/* Discard zero bytes */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_tmp = iov;
iov_cnt_tmp = iov_cnt;
iov_discard_front_undoable(&iov_tmp, &iov_cnt_tmp, 0, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard more bytes than vector size */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_tmp = iov;
iov_cnt_tmp = iov_cnt;
size = iov_size(iov, iov_cnt);
iov_discard_front_undoable(&iov_tmp, &iov_cnt_tmp, size + 1, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard entire vector */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_tmp = iov;
iov_cnt_tmp = iov_cnt;
size = iov_size(iov, iov_cnt);
iov_discard_front_undoable(&iov_tmp, &iov_cnt_tmp, size, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard within first element */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_tmp = iov;
iov_cnt_tmp = iov_cnt;
size = g_test_rand_int_range(1, iov->iov_len);
iov_discard_front_undoable(&iov_tmp, &iov_cnt_tmp, size, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard entire first element */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_tmp = iov;
iov_cnt_tmp = iov_cnt;
iov_discard_front_undoable(&iov_tmp, &iov_cnt_tmp, iov->iov_len, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard within second element */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_tmp = iov;
iov_cnt_tmp = iov_cnt;
size = iov->iov_len + g_test_rand_int_range(1, iov[1].iov_len);
iov_discard_front_undoable(&iov_tmp, &iov_cnt_tmp, size, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
}
static void test_discard_back(void)
{
struct iovec *iov;
@ -404,6 +491,82 @@ static void test_discard_back(void)
iov_free(iov, iov_cnt);
}
static void test_discard_back_undo(void)
{
IOVDiscardUndo undo;
struct iovec *iov;
struct iovec *iov_orig;
unsigned int iov_cnt;
unsigned int iov_cnt_tmp;
size_t size;
/* Discard zero bytes */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_cnt_tmp = iov_cnt;
iov_discard_back_undoable(iov, &iov_cnt_tmp, 0, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard more bytes than vector size */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_cnt_tmp = iov_cnt;
size = iov_size(iov, iov_cnt);
iov_discard_back_undoable(iov, &iov_cnt_tmp, size + 1, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard entire vector */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_cnt_tmp = iov_cnt;
size = iov_size(iov, iov_cnt);
iov_discard_back_undoable(iov, &iov_cnt_tmp, size, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard within last element */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_cnt_tmp = iov_cnt;
size = g_test_rand_int_range(1, iov[iov_cnt - 1].iov_len);
iov_discard_back_undoable(iov, &iov_cnt_tmp, size, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard entire last element */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_cnt_tmp = iov_cnt;
size = iov[iov_cnt - 1].iov_len;
iov_discard_back_undoable(iov, &iov_cnt_tmp, size, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
/* Discard within second-to-last element */
iov_random(&iov, &iov_cnt);
iov_orig = g_memdup(iov, sizeof(iov[0]) * iov_cnt);
iov_cnt_tmp = iov_cnt;
size = iov[iov_cnt - 1].iov_len +
g_test_rand_int_range(1, iov[iov_cnt - 2].iov_len);
iov_discard_back_undoable(iov, &iov_cnt_tmp, size, &undo);
iov_discard_undo(&undo);
assert(iov_equals(iov, iov_orig, iov_cnt));
g_free(iov_orig);
iov_free(iov, iov_cnt);
}
int main(int argc, char **argv)
{
g_test_init(&argc, &argv, NULL);
@ -412,5 +575,7 @@ int main(int argc, char **argv)
g_test_add_func("/basic/iov/io", test_io);
g_test_add_func("/basic/iov/discard-front", test_discard_front);
g_test_add_func("/basic/iov/discard-back", test_discard_back);
g_test_add_func("/basic/iov/discard-front-undo", test_discard_front_undo);
g_test_add_func("/basic/iov/discard-back-undo", test_discard_back_undo);
return g_test_run();
}

50
util/iov.c
View File

@ -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;