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authorDr. David Alan Gilbert <dgilbert@redhat.com>2015-11-05 18:10:35 +0000
committerJuan Quintela <quintela@redhat.com>2015-11-10 14:51:48 +0100
commit9504fb510c87c3dd6fe2e9a25e84c1426672f226 (patch)
treef6fa039d3c9411ccaadf729104e9e79a2d84756d /migration
parent42e2aa56372291d35345fcec85d5da2004c8b57c (diff)
downloadhqemu-9504fb510c87c3dd6fe2e9a25e84c1426672f226.zip
hqemu-9504fb510c87c3dd6fe2e9a25e84c1426672f226.tar.gz
Add qemu_get_buffer_in_place to avoid copies some of the time
qemu_get_buffer always copies the data it reads to a users buffer, however in many cases the file buffer inside qemu_file could be given back to the caller, avoiding the copy. This isn't always possible depending on the size and alignment of the data. Thus 'qemu_get_buffer_in_place' either copies the data to a supplied buffer or updates a pointer to the internal buffer if convenient. Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Reviewed-by: Juan Quintela <quintela@redhat.com> Signed-off-by: Juan Quintela <quintela@redhat.com>
Diffstat (limited to 'migration')
-rw-r--r--migration/qemu-file.c37
1 files changed, 37 insertions, 0 deletions
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index df49023..e41a677 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -434,6 +434,43 @@ size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t size)
}
/*
+ * Read 'size' bytes of data from the file.
+ * 'size' can be larger than the internal buffer.
+ *
+ * The data:
+ * may be held on an internal buffer (in which case *buf is updated
+ * to point to it) that is valid until the next qemu_file operation.
+ * OR
+ * will be copied to the *buf that was passed in.
+ *
+ * The code tries to avoid the copy if possible.
+ *
+ * It will return size bytes unless there was an error, in which case it will
+ * return as many as it managed to read (assuming blocking fd's which
+ * all current QEMUFile are)
+ *
+ * Note: Since **buf may get changed, the caller should take care to
+ * keep a pointer to the original buffer if it needs to deallocate it.
+ */
+size_t qemu_get_buffer_in_place(QEMUFile *f, uint8_t **buf, size_t size)
+{
+ if (size < IO_BUF_SIZE) {
+ size_t res;
+ uint8_t *src;
+
+ res = qemu_peek_buffer(f, &src, size, 0);
+
+ if (res == size) {
+ qemu_file_skip(f, res);
+ *buf = src;
+ return res;
+ }
+ }
+
+ return qemu_get_buffer(f, *buf, size);
+}
+
+/*
* Peeks a single byte from the buffer; this isn't guaranteed to work if
* offset leaves a gap after the previous read/peeked data.
*/
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