Re: [PATCH v5 06/14] migration/qemu-file: Add qemu_file_get_to_fd()

[Avihai Horon]

On 09/01/2023 13:20, Cédric Le Goater wrote:
> External email: Use caution opening links or attachments
>
>
> On 12/29/22 12:03, Avihai Horon wrote:
> > Add new function qemu_file_get_to_fd() that allows reading data from
> > QEMUFile and writing it straight into a given fd.
> >
> > This will be used later in VFIO migration code.
> >
> > Signed-off-by: Avihai Horon <avihaih@nvidia.com>
> > Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
> > ---
> >   migration/qemu-file.h |  1 +
> >   migration/qemu-file.c | 34 ++++++++++++++++++++++++++++++++++
> >   2 files changed, 35 insertions(+)
> >
> > diff --git a/migration/qemu-file.h b/migration/qemu-file.h
> > index fa13d04d78..9d0155a2a1 100644
> > --- a/migration/qemu-file.h
> > +++ b/migration/qemu-file.h
> > @@ -148,6 +148,7 @@ int qemu_file_shutdown(QEMUFile *f);
> >   QEMUFile *qemu_file_get_return_path(QEMUFile *f);
> >   void qemu_fflush(QEMUFile *f);
> >   void qemu_file_set_blocking(QEMUFile *f, bool block);
> > +int qemu_file_get_to_fd(QEMUFile *f, int fd, size_t size);
> >
> >   void ram_control_before_iterate(QEMUFile *f, uint64_t flags);
> >   void ram_control_after_iterate(QEMUFile *f, uint64_t flags);
> > diff --git a/migration/qemu-file.c b/migration/qemu-file.c
> > index 2d5f74ffc2..79303c9d34 100644
> > --- a/migration/qemu-file.c
> > +++ b/migration/qemu-file.c
> > @@ -940,3 +940,37 @@ QIOChannel *qemu_file_get_ioc(QEMUFile *file)
> >   {
> >       return file->ioc;
> >   }
> > +
> > +/*
> > + * Read size bytes from QEMUFile f and write them to fd.
> > + */
> > +int qemu_file_get_to_fd(QEMUFile *f, int fd, size_t size)
> > +{
> > +    while (size) {
> > +        size_t pending = f->buf_size - f->buf_index;
> > +        ssize_t rc;
> > +
> > +        if (!pending) {
> > +            rc = qemu_fill_buffer(f);
> > +            if (rc < 0) {
> > +                return rc;
> > +            }
> > +            if (rc == 0) {
> > +                return -1;
>
> Given the call stack, -1 would be interpreted  as EPERM. May be EIO 
> instead ?
Sure.

I will also change write (down below) to return -errno instead of rc on 
error.

> C.
>
> > +            }
> > +            continue;
> > +        }
> > +
> > +        rc = write(fd, f->buf + f->buf_index, MIN(pending, size));
> > +        if (rc < 0) {
> > +            return rc;
> > +        }
> > +        if (rc == 0) {
> > +            return -1;
> > +        }
> > +        f->buf_index += rc;
> > +        size -= rc;
> > +    }
> > +
> > +    return 0;
> > +}