From 54e269009099cdc9483be115f1e12d56ad459c5e Mon Sep 17 00:00:00 2001 From: Jeff Cody Date: Wed, 25 Jun 2014 15:40:10 -0400 Subject: block: extend block-commit to accept a string for the backing file On some image chains, QEMU may not always be able to resolve the filenames properly, when updating the backing file of an image after a block commit. For instance, certain relative pathnames may fail, or drives may have been specified originally by file descriptor (e.g. /dev/fd/???), or a relative protocol pathname may have been used. In these instances, QEMU may lack the information to be able to make the correct choice, but the user or management layer most likely does have that knowledge. With this extension to the block-commit api, the user is able to change the backing file of the overlay image as part of the block-commit operation. This allows the change to be 'safe', in the sense that if the attempt to write the overlay image metadata fails, then the block-commit operation returns failure, without disrupting the guest. If the commit top is the active layer, then specifying the backing file string will be treated as an error (there is no overlay image to modify in that case). If a backing file string is not specified in the command, the backing file string to use is determined in the same manner as it was previously. Reviewed-by: Eric Blake Signed-off-by: Jeff Cody Reviewed-by: Kevin Wolf Signed-off-by: Stefan Hajnoczi --- blockdev.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) (limited to 'blockdev.c') diff --git a/blockdev.c b/blockdev.c index 57373d3661..48315e86c0 100644 --- a/blockdev.c +++ b/blockdev.c @@ -1915,6 +1915,7 @@ void qmp_block_stream(const char *device, bool has_base, void qmp_block_commit(const char *device, bool has_base, const char *base, bool has_top, const char *top, + bool has_backing_file, const char *backing_file, bool has_speed, int64_t speed, Error **errp) { @@ -1980,11 +1981,16 @@ void qmp_block_commit(const char *device, } if (top_bs == bs) { + if (has_backing_file) { + error_setg(errp, "'backing-file' specified," + " but 'top' is the active layer"); + return; + } commit_active_start(bs, base_bs, speed, on_error, block_job_cb, bs, &local_err); } else { commit_start(bs, base_bs, top_bs, speed, on_error, block_job_cb, bs, - &local_err); + has_backing_file ? backing_file : NULL, &local_err); } if (local_err != NULL) { error_propagate(errp, local_err); -- cgit v1.2.3