On Thu, May 23, 2013 at 01:44:40PM -0400, Corey Bryant wrote:
This patch series provides VNVRAM persistent storage support that
QEMU can use internally. The initial target user will be a software
vTPM 1.2 backend that needs to store keys in VNVRAM and be able to
reboot/migrate and retain the keys.
This support uses QEMU's block driver to provide persistent storage
by reading/writing VNVRAM data from/to a drive image. The VNVRAM
drive image is provided with the -drive command line option just like
any other drive image and the vnvram_create() API will find it.
The APIs allow for VNVRAM entries to be registered, one at a time,
each with a maximum blob size. Entry blobs can then be read/written
from/to an entry on the drive. Here's an example of usage:
VNVRAM *vnvram;
int errcode
const VNVRAMEntryName entry_name;
const char *blob_w = "blob data";
char *blob_r;
uint32_t blob_r_size;
vnvram = vnvram_create("drive-ide0-0-0", false, &errcode);
strcpy((char *)entry_name, "first-entry");
VNVRAMEntryName is very prone to buffer overflow. I hope real code
doesn't use strcpy(). The cast is ugly, please don't hide the type.
vnvram_register_entry(vnvram, &entry_name, 1024);
vnvram_write_entry(vnvram, &entry_name, (char *)blob_w, strlen(blob_w)+1);
vnvram_read_entry(vnvram, &entry_name, &blob_r, &blob_r_size);
These are synchronous functions. If I/O is involved then this is a
problem: QEMU will be blocked waiting for host I/O to complete and the
big QEMU lock is held. This can cause poor guest interactivity and poor
scalability because vcpus cannot make progress, neither can the QEMU
monitor respond.