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Revision 75c439bc

ID75c439bc65c07d76f5e74c734ed5432bc6114a3b

Added by Hans de Goede over 7 years ago

spice-qemu-char: vmc_write: Don't write more bytes then we're asked too

This one took me eons to debug, but I've finally found it now, oh well.

The usage of the MIN macro in this line:
last_out = MIN);

Causes qemu_chr_be_can_write to be called twice, since the MIN macro
evaluates its arguments twice (bad MIN macro, bad!). And the result of
the call can change between the 2 calls since the guest may have consumed
some data from the virtio ringbuffer between the calls!

When this happens it is possible for qemu_chr_be_can_write to return less
then len in the call made for the comparision, and then to return more then
len in the actual call for the return-value of MIN, after which we will end
up writing len data + some extra garbage, not good.

This patch fixes this by only calling qemu_chr_be_can_write once.

Signed-off-by: Hans de Goede <>
Signed-off-by: Gerd Hoffmann <>

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