So this is failing I/O that iterates over a channel.
I was tracking down the len, pending and pos used.
I found that this is not completely broken (like no access or generla I/O error)
It starts at pos 0 and iterated with varying offsets, but works for quite some
time.
Example:
[...]
Thread 1 "qemu-system-x86" hit Breakpoint 2, qemu_fill_buffer
(f=f@entry=0xd3b66f3c00) at ./migration/qemu-file.c:295
295 if (len > 0) {
$11183 = 28728
$11184 = 4040
$11185 = {ops = 0xd3b3d740a0 <channel_input_ops>, hooks = 0x0, opaque =
0xd3b75ee490, bytes_xfer = 0, xfer_limit = 0, pos = 107130146,
buf_index = 0, buf_size = 4040,
buf = "\v\327\a\000\021\000\[...]\000"...,
may_free = {0}, iov = {{iov_base = 0x0, iov_len = 0} <repeats 64 times>},
iovcnt = 0, last_error = 0}
[...]
Well you could see the whole file read passing by one by one buffer
Yet this isn't particularly fast, so track the one that has len==0
(gdb) b ./migration/qemu-file.c:295 if len == 0
And I got it as:
(gdb) p *f
$11195 = {ops = 0xd3b3d740a0 <channel_input_ops>, hooks = 0x0, opaque =
0xd3b75ee490, bytes_xfer = 0, xfer_limit = 0, pos = 319638837,
buf_index = 0, buf_size = 0, buf = '\000' <repeats 5504 times>..., may_free =
{0}, iov = {{iov_base = 0x0, iov_len = 0} <repeats 64 times>},
iovcnt = 0, last_error = 0}
Here pending == 0 so buf_size = 0 as well also pos is further down
incremented to 319638837.
Checking in detail I found that I had pending=0 and buf_size=0 as well as non
aligned pos entried, but they worked.
So I excluded the buf_size=0/pending=0 as well as the alignment as reasons.
Maybe it just iterates pos out of the range that is working?
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https://bugs.launchpad.net/bugs/1711602
Title:
--copy-storage-all failing with qemu 2.10
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