Commit 97221400 authored by Alexander Graf's avatar Alexander Graf Committed by Juan Quintela
Browse files

qemu-file: Add fast ftell code path 



For ftell we flush the output buffer to ensure that we don't have anything
lingering in our internal buffers. This is a very safe thing to do.

However, with the dynamic size measurement that the dynamic vmstate
description will bring this would turn out quite slow.

Instead, we can fast path this specific measurement and just take the
internal buffers into account when telling the kernel our position.

I'm sure I overlooked some corner cases where this doesn't work, so
instead of tuning the safe, existing version, this patch adds a fast
variant of ftell that gets used by the dynamic vmstate description code
which isn't critical when it fails.

Signed-off-by: default avatarAlexander Graf <agraf@suse.de>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Signed-off-by: default avatarAmit Shah <amit.shah@redhat.com>
Signed-off-by: default avatarJuan Quintela <quintela@redhat.com>
parent 190c882c

include/migration/qemu-file.h

+1 −0
Original line number Diff line number Diff line
@@ -121,6 +121,7 @@ QEMUFile *qemu_bufopen(const char *mode, QEMUSizedBuffer *input); 
int qemu_get_fd(QEMUFile *f);

int qemu_fclose(QEMUFile *f);

int64_t qemu_ftell(QEMUFile *f);

int64_t qemu_ftell_fast(QEMUFile *f);

void qemu_put_buffer(QEMUFile *f, const uint8_t *buf, int size);

void qemu_put_byte(QEMUFile *f, int v);

/*

migration/qemu-file.c

+16 −0
Original line number Diff line number Diff line
@@ -452,6 +452,22 @@ int qemu_get_byte(QEMUFile *f) 
    return result;

}



int64_t qemu_ftell_fast(QEMUFile *f)

{

    int64_t ret = f->pos;

    int i;



    if (f->ops->writev_buffer) {

        for (i = 0; i < f->iovcnt; i++) {

            ret += f->iov[i].iov_len;

        }

    } else {

        ret += f->buf_index;

    }



    return ret;

}



int64_t qemu_ftell(QEMUFile *f)

{

    qemu_fflush(f);