From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49803) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yi4Ge-0006AH-SY for qemu-devel@nongnu.org; Tue, 14 Apr 2015 13:04:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Yi4Gb-0002It-8V for qemu-devel@nongnu.org; Tue, 14 Apr 2015 13:04:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34353) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yi4Gb-0002Ib-1z for qemu-devel@nongnu.org; Tue, 14 Apr 2015 13:04:53 -0400 From: "Dr. David Alan Gilbert (git)" Date: Tue, 14 Apr 2015 18:03:34 +0100 Message-Id: <1429031053-4454-9-git-send-email-dgilbert@redhat.com> In-Reply-To: <1429031053-4454-1-git-send-email-dgilbert@redhat.com> References: <1429031053-4454-1-git-send-email-dgilbert@redhat.com> Subject: [Qemu-devel] [PATCH v6 08/47] Add qemu_get_buffer_less_copy to avoid copies some of the time List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: aarcange@redhat.com, yamahata@private.email.ne.jp, quintela@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com, david@gibson.dropbear.id.au, yayanghy@cn.fujitsu.com From: "Dr. David Alan Gilbert" 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_less_copy' 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 --- include/migration/qemu-file.h | 2 ++ migration/qemu-file.c | 45 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 47 insertions(+) diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h index 3fe545e..4cac58f 100644 --- a/include/migration/qemu-file.h +++ b/include/migration/qemu-file.h @@ -159,6 +159,8 @@ void qemu_put_be32(QEMUFile *f, unsigned int v); void qemu_put_be64(QEMUFile *f, uint64_t v); int qemu_peek_buffer(QEMUFile *f, uint8_t **buf, int size, size_t offset); int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int size); +int qemu_get_buffer_less_copy(QEMUFile *f, uint8_t **buf, int size); + /* * Note that you can only peek continuous bytes from where the current pointer * is; you aren't guaranteed to be able to peak to +n bytes unless you've diff --git a/migration/qemu-file.c b/migration/qemu-file.c index 8dc5767..ec3a598 100644 --- a/migration/qemu-file.c +++ b/migration/qemu-file.c @@ -426,6 +426,51 @@ int qemu_get_buffer(QEMUFile *f, uint8_t *buf, int 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) + */ +int qemu_get_buffer_less_copy(QEMUFile *f, uint8_t **buf, int size) +{ + int pending = size; + int done = 0; + bool first = true; + + while (pending > 0) { + int res; + uint8_t *src; + + res = qemu_peek_buffer(f, &src, MIN(pending, IO_BUF_SIZE), 0); + if (res == 0) { + return done; + } + qemu_file_skip(f, res); + done += res; + pending -= res; + if (first && res == size) { + *buf = src; + return done; + } else { + first = false; + memcpy(buf, src, res); + buf += res; + } + } + return done; +} + +/* * Peeks a single byte from the buffer; this isn't guaranteed to work if * offset leaves a gap after the previous read/peeked data. */ -- 2.1.0