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iov: add qemu_iovec_concat_iov()

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The qemu_iovec_concat() function copies a subset of a QEMUIOVector.  The
new qemu_iovec_concat_iov() function does the same for a iov/cnt pair.

It is easy to define qemu_iovec_concat() in terms of
qemu_iovec_concat_iov().  The existing code is mostly unchanged, except
for the assertion src->size >= soffset, which cannot be efficiently
checked upfront on a iov/cnt pair.  Instead we assert upon hitting the
end of src with an unsatisfied soffset.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2012-11-22 16:06:06 +01:00
parent 8962e44fe4
commit 530c0bbd73
2 changed files with 34 additions and 16 deletions
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3
include/qemu-common.h
View File

@ -329,6 +329,9 @@ void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov);
void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
void qemu_iovec_concat(QEMUIOVector *dst,
QEMUIOVector *src, size_t soffset, size_t sbytes);
void qemu_iovec_concat_iov(QEMUIOVector *dst,
struct iovec *src_iov, unsigned int src_cnt,
size_t soffset, size_t sbytes);
void qemu_iovec_destroy(QEMUIOVector *qiov);
void qemu_iovec_reset(QEMUIOVector *qiov);
size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,

47
iov.c
View File

@ -288,6 +288,36 @@ void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len)
++qiov->niov;
}
/*
* Concatenates (partial) iovecs from src_iov to the end of dst.
* It starts copying after skipping `soffset' bytes at the
* beginning of src and adds individual vectors from src to
* dst copies up to `sbytes' bytes total, or up to the end
* of src_iov if it comes first. This way, it is okay to specify
* very large value for `sbytes' to indicate "up to the end
* of src".
* Only vector pointers are processed, not the actual data buffers.
*/
void qemu_iovec_concat_iov(QEMUIOVector *dst,
struct iovec *src_iov, unsigned int src_cnt,
size_t soffset, size_t sbytes)
{
int i;
size_t done;
assert(dst->nalloc != -1);
for (i = 0, done = 0; done < sbytes && i < src_cnt; i++) {
if (soffset < src_iov[i].iov_len) {
size_t len = MIN(src_iov[i].iov_len - soffset, sbytes - done);
qemu_iovec_add(dst, src_iov[i].iov_base + soffset, len);
done += len;
soffset = 0;
} else {
soffset -= src_iov[i].iov_len;
}
}
assert(soffset == 0); /* offset beyond end of src */
}
/*
* Concatenates (partial) iovecs from src to the end of dst.
* It starts copying after skipping `soffset' bytes at the
@ -301,22 +331,7 @@ void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len)
void qemu_iovec_concat(QEMUIOVector *dst,
QEMUIOVector *src, size_t soffset, size_t sbytes)
{
int i;
size_t done;
struct iovec *siov = src->iov;
assert(dst->nalloc != -1);
assert(src->size >= soffset);
for (i = 0, done = 0; done < sbytes && i < src->niov; i++) {
if (soffset < siov[i].iov_len) {
size_t len = MIN(siov[i].iov_len - soffset, sbytes - done);
qemu_iovec_add(dst, siov[i].iov_base + soffset, len);
done += len;
soffset = 0;
} else {
soffset -= siov[i].iov_len;
}
}
/* return done; */
qemu_iovec_concat_iov(dst, src->iov, src->niov, soffset, sbytes);
}
void qemu_iovec_destroy(QEMUIOVector *qiov)