Hello, On Monday, April 07, 2025 08:47 CEST, Prasad Pandit <ppan...@redhat.com> wrote:
> * If seeking is managed internally by pread(2)/pwrite(2) and co. > functions, then that is independent of the > 'QIO_CHANNEL_FEATURE_SEEKABLE' flag; This flag is QEMU specific, it is > not available outside of QEMU/io/ system. pread(2)/pwrite(2) are > standard C library functions. > * Another question is: will pread(2)/pwrite(2) functions work the same > if we don't set the 'QIO_CHANNEL_FEATURE_SEEKABLE' flag? > > (what I'm trying to say is: it is not clear how setting > '*_FEATURE_SEEKABLE' flag helps in case of QIOChannelBlock class) As you said the capability is used internally. Its goal is to signal to other QEMU code that the QIOChannel is seekable. 'qio_channel_pwritev' and 'qio_channel_preadv' can be used only if the QIOChannel has the 'QIO_CHANNEL_FEATURE_SEEKABLE' capability. The mapped-ram migration checks if the channel has this capability because it uses the aforementioned functions. Without the capability and the functions implemented in this patch, the mapped-ram migration won't work with QIOChannelBlock. You can have a look at the patch where those functions were introduced here [0]. Best, Marco [0] https://lore.kernel.org/qemu-devel/20240229153017.2221-4-faro...@suse.de/
