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** Changed in: qemu
Status: New => Incomplete
--
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1893003
Title:
qemu linux-user doesn't translate host/target data for iovec I/O
Status in QEMU:
Incomplete
Bug description:
When using iovec I/O functions (like `readv`), no data translation
happens. I'm hitting this issue with libevent upon constructing a
bufferevent over an inotify descriptor, and then building for either
ppc64 or s390x (both big-endian) on x86_64 (little-endian) and running
resulting code with qemu-ppc64 or qemu-s390x on Gentoo using latest
QEMU version available (5.0.0-r2).
The code in question is in
https://github.com/transmission/transmission/blob/master/libtransmission
/watchdir-inotify.c (`tr_watchdir_inotify_new`,
`tr_watchdir_inotify_on_event`).
While `read` syscall is handled properly, `readv` (which libevent is
using in my case) doesn't have any logic to call
`host_to_target_data_inotify` or any other translation function,
leaving inotify data unchanged (with values in little-endian), which
then leads to unit test failures. Quoting `do_syscall1` implementation
bits for the reference:
---8<---begin---
case TARGET_NR_read:
if (arg2 == 0 && arg3 == 0) {
return get_errno(safe_read(arg1, 0, 0));
} else {
if (!(p = lock_user(VERIFY_WRITE, arg2, arg3, 0)))
return -TARGET_EFAULT;
ret = get_errno(safe_read(arg1, p, arg3));
if (ret >= 0 &&
fd_trans_host_to_target_data(arg1)) {
ret = fd_trans_host_to_target_data(arg1)(p, ret);
}
unlock_user(p, arg2, ret);
}
return ret;
...
case TARGET_NR_readv:
{
struct iovec *vec = lock_iovec(VERIFY_WRITE, arg2, arg3, 0);
if (vec != NULL) {
ret = get_errno(safe_readv(arg1, vec, arg3));
unlock_iovec(vec, arg2, arg3, 1);
} else {
ret = -host_to_target_errno(errno);
}
}
return ret;
---8<---end---
To reiterate, the issue is not only with `readv` but with other iovec
functions as well.
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