[RFC PATCH v3 01/30] io: add and implement QIO_CHANNEL_FEATURE_SEEKABLE for channel file

[Fabiano Rosas <farosas@suse.de>]

From: Nikolay Borisov <nborisov@suse.com>

Add a generic QIOChannel feature SEEKABLE which would be used by the
qemu_file* apis. For the time being this will be only implemented for
file channels.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/io/channel.h | 1 +
 io/channel-file.c    | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/include/io/channel.h b/include/io/channel.h
index 5f9dbaab65..fcb19fd672 100644
--- a/include/io/channel.h
+++ b/include/io/channel.h
@@ -44,6 +44,7 @@ enum QIOChannelFeature {
     QIO_CHANNEL_FEATURE_LISTEN,
     QIO_CHANNEL_FEATURE_WRITE_ZERO_COPY,
     QIO_CHANNEL_FEATURE_READ_MSG_PEEK,
+    QIO_CHANNEL_FEATURE_SEEKABLE,
 };
 
 
diff --git a/io/channel-file.c b/io/channel-file.c
index 4a12c61886..f91bf6db1c 100644
--- a/io/channel-file.c
+++ b/io/channel-file.c
@@ -36,6 +36,10 @@ qio_channel_file_new_fd(int fd)
 
     ioc->fd = fd;
 
+    if (lseek(fd, 0, SEEK_CUR) != (off_t)-1) {
+        qio_channel_set_feature(QIO_CHANNEL(ioc), QIO_CHANNEL_FEATURE_SEEKABLE);
+    }
+
     trace_qio_channel_file_new_fd(ioc, fd);
 
     return ioc;
@@ -60,6 +64,10 @@ qio_channel_file_new_path(const char *path,
         return NULL;
     }
 
+    if (lseek(ioc->fd, 0, SEEK_CUR) != (off_t)-1) {
+        qio_channel_set_feature(QIO_CHANNEL(ioc), QIO_CHANNEL_FEATURE_SEEKABLE);
+    }
+
     trace_qio_channel_file_new_path(ioc, path, flags, mode, ioc->fd);
 
     return ioc;
-- 
2.35.3