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[Qemu-devel] getfd monitor command broken

From: Ed Swierk
Subject: [Qemu-devel] getfd monitor command broken
Date: Fri, 19 Feb 2010 10:21:41 -0800

Commit c62313bbdc48f72e93fa8196f2fff96ba35e4e9d seems to have broken
the getfd monitor command in qemu 0.12.

tcp_chr_read() calls tcp_chr_recv(), which checks whether the received
message includes an SCM_RIGHTS header, and if so, stores the received
fd in the CharDriverState struct. tcp_chr_read() passes the received
data to the monitor via qemu_chr_read(), and then closes the stored

Previously, tcp_chr_read() would receive the entire getfd command in
one message (perhaps by sheer luck), allowing the monitor to call
qemu_chr_get_msgfd() to obtain the stored fd before it disappeared.
Now that tcp_chr_read() receives only 1 byte at a time, the stored fd
vanishes when it receives byte 2.

I'm too confused by this control flow to suggest a proper solution,
but commenting out the "if (s->msgfd != -1)" block in tcp_chr_read()
at least makes the problem go away.


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