Ok, so what I was missing was how eofcat works.
Let's simplify the reproducer for real. I assume this used to work on
older kernels, can someone confirm?
0/ some random 9p mount in a VM
1/ create 'foo' empty file (either host or VM doesn't matter)
: > foo
2/ in VM, keep reading it until content appears:
while true; do read content; if [ -n "$content" ]; then echo $content;
break; fi; done < foo
3/ on host, write some data:
echo foo >> foo
This doesn't get any data in VM, and I assume it used to work, and it'll
likely work with your patch -- just doing a stat or anything in the vm
unblocks it.
As said in the previous comment, read shouldn't assume the file size and
that'll solve the problem.
v9fs_file_read_iter() is called with an appropriate size... So is
netfs_unbuffered_read_iter() and netfs_begin_read() but the problem is that
netfs_begin_read() skips the read altogether as it doesn't match its assumption
for i_size
In unbuffered mode, it shouldn't match i_size and just stop when read
returns 0.
the netfs read request was allocated with
netfs_alloc_request(NETFS_DIO_READ) so at that point we still know it's
uncached, but that information seems to be lost for netfs_begin_read()
and I'm not sure what is best to check.
@David -- now we have a simpler reproducer & know exactly what's wrong,
could you look at this this week?
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https://bugs.launchpad.net/bugs/2056461
Title:
autopkgtest-virt-qemu on noble images sometimes hangs doing copydown
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