Re: [PATCH v6 1/2] io: Add support for MSG_PEEK for socket channel

[Juan Quintela]

Daniel P. Berrangé <berrange@redhat.com> wrote:
> On Thu, Feb 02, 2023 at 01:22:12PM +0100, Juan Quintela wrote:
>> "manish.mishra" <manish.mishra@nutanix.com> wrote:
>> > MSG_PEEK peeks at the channel, The data is treated as unread and
>> > the next read shall still return this data. This support is
>> > currently added only for socket class. Extra parameter 'flags'
>> > is added to io_readv calls to pass extra read flags like MSG_PEEK.
>> >
>> > Reviewed-by: Peter Xu <peterx@redhat.com>
>> > Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
>> > Suggested-by: Daniel P. Berrange <berrange@redhat.com>
>> > Signed-off-by: manish.mishra <manish.mishra@nutanix.com>
>> 
>> 
>> This change breaks RDMA migration.
>> 
>> FAILED: libcommon.fa.p/migration_rdma.c.o
>> cc -m64 -mcx16 -Ilibcommon.fa.p -I/usr/include/pixman-1 
>> -I/usr/include/libpng16 -I/usr/include/spice-server -I/usr/include/spice-1 
>> -I/usr/include/cacard -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include 
>> -I/usr/include/sysprof-4 -I/usr/include/nss3 -I/usr/include/nspr4 
>> -I/usr/include/PCSC -I/usr/include/p11-kit-1 -I/usr/include/libusb-1.0 
>> -I/usr/include/SDL2 -I/usr/include/libmount -I/usr/include/blkid 
>> -I/usr/include/gio-unix-2.0 -I/usr/include/slirp -fdiagnostics-color=auto 
>> -Wall -Winvalid-pch -Werror -std=gnu11 -O2 -g -isystem 
>> /mnt/code/qemu/full/linux-headers -isystem linux-headers -iquote . -iquote 
>> /mnt/code/qemu/full -iquote /mnt/code/qemu/full/include -iquote 
>> /mnt/code/qemu/full/tcg/i386 -pthread -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 
>> -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE 
>> -fno-strict-aliasing -fno-common -fwrapv -Wundef -Wwrite-strings 
>> -Wmissing-prototypes -Wstrict-prototypes -Wredundant-decls 
>> -Wold-style-declaration -Wold-style-definition -Wtype-limits 
>> -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wempty-body 
>> -Wnested-externs -Wendif-labels -Wexpansion-to-defined 
>> -Wimplicit-fallthrough=2 -Wmissing-format-attribute 
>> -Wno-missing-include-dirs -Wno-shift-negative-value -Wno-psabi 
>> -fstack-protector-strong -fPIE -D_REENTRANT -Wno-undef 
>> -DSTRUCT_IOVEC_DEFINED -MD -MQ libcommon.fa.p/migration_rdma.c.o -MF 
>> libcommon.fa.p/migration_rdma.c.o.d -o libcommon.fa.p/migration_rdma.c.o -c 
>> ../../../../mnt/code/qemu/full/migration/rdma.c
>> ../../../../mnt/code/qemu/full/migration/rdma.c: In function 
>> ‘qio_channel_rdma_class_init’:
>> ../../../../mnt/code/qemu/full/migration/rdma.c:4020:25: error: assignment 
>> to ‘ssize_t (*)(QIOChannel *, const struct iovec *, size_t,  int **, size_t 
>> *, int,  Error **)’ {aka ‘long int (*)(QIOChannel *, const struct iovec *, 
>> long unsigned int,  int **, long unsigned int *, int,  Error **)’} from 
>> incompatible pointer type ‘ssize_t (*)(QIOChannel *, const struct iovec *, 
>> size_t,  int **, size_t *, Error **)’ {aka ‘long int (*)(QIOChannel *, const 
>> struct iovec *, long unsigned int,  int **, long unsigned int *, Error **)’} 
>> [-Werror=incompatible-pointer-types]
>>  4020 |     ioc_klass->io_readv = qio_channel_rdma_readv;
>>       |                         ^
>> cc1: all warnings being treated as errors
>> 
>> And I don't really know how to fix it, because the problem is that rdma
>> don't use qio_channel_readv_full() at all.
>
> Likely qio_channel_rdma_readv just adds the 'int flags' param added.
> It doesn't need to actually do anything with the flags as they are
> checked before

I can do that.  That would fix the compilation issue.

But will rdma work?  Because it fakes a qio channel, so what is going to
implement the MSG_PEEK functionality for it?  It don't end calling
recv() at all.


Later, Juan.