On 1/15/19 3:44 AM, Vladimir Sementsov-Ogievskiy wrote: > 12.01.2019 20:57, Eric Blake wrote: >> We only had two callers to nbd_export_new; qemu-nbd.c always >> passed a valid offset/length pair (because it already checked >> the file length, to ensure that offset was in bounds), while >> blockdev-nbd always passed 0/-1. Then nbd_export_new reduces >> the size to a multiple of BDRV_SECTOR_SIZE (can only happen >> when offset is not sector-aligned, since bdrv_getlength() >> currently rounds up), which can result in offset being greater >> than the enforced length, but that's not fatal (the server >> rejects client requests that exceed the advertised length). >> >> However, I'm finding it easier to work with the code if we are >> consistent on having both callers pass in a valid length, and >> just assert that things are sane in nbd_export_new. >> >> Signed-off-by: Eric Blake <[email protected]> >>
>> +++ b/nbd/server.c
>> @@ -1499,13 +1499,8 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t
>> dev_offset, off_t size,
>> exp->name = g_strdup(name);
>> exp->description = g_strdup(description);
>> exp->nbdflags = nbdflags;
>> - exp->size = size < 0 ? blk_getlength(blk) : size;
>> - if (exp->size < 0) {
>> - error_setg_errno(errp, -exp->size,
>> - "Failed to determine the NBD export's length");
>> - goto fail;
>> - }
>> - exp->size -= exp->size % BDRV_SECTOR_SIZE;
>> + assert(dev_offset <= size);
>
> @size is not size of the image, but size of the export, so it may be less
> than dev_offset
> (qemu-nbd.c do "fd_size -= dev_offset" before "nbd_export_new(bs, dev_offset,
> fd_size, "
But the assert is fine because patch 3/19 fixed qemu-nbd.c to never pass
in dev_offset larger than size (it fails up front if dev_offset is out
of bounds, whether from the -o command line option or from what it read
from the partition header with the -P command line option).
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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