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Cygwin: pipes: fix POSIX requirement for non-blocking pipe writes 

POSIX requires atomicity for non-blocking writes <= PIPE_BUF bytes
and writing of at least 1 byte if any buffer space is left.
Windows NtWriteFile returns STATUS_SUCCESS and "0 bytes written"
if the write doesn't match buffer space.  Fix this discrepancy.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2021-09-03 10:45:49 +02:00
parent fcccc4b743
commit a5b2c735e6
1 changed files with 37 additions and 14 deletions
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51
winsup/cygwin/fhandler_pipe.cc
View File

@ -313,7 +313,6 @@ fhandler_pipe::raw_read (void *ptr, size_t& len)
ssize_t __reg3
fhandler_pipe::raw_write (const void *ptr, size_t len)
{
ssize_t ret = -1;
size_t nbytes = 0;
ULONG chunk;
NTSTATUS status = STATUS_SUCCESS;
@ -351,9 +350,36 @@ fhandler_pipe::raw_write (const void *ptr, size_t len)
len1 = chunk;
else
len1 = (ULONG) left;
nbytes_now = 0;
status = NtWriteFile (get_handle (), evt, NULL, NULL, &io,
(PVOID) ptr, len1, NULL, NULL);
/* NtWriteFile returns success with # of bytes written == 0 if writing
on a non-blocking pipe fails because the pipe buffer doesn't have
sufficient space.
POSIX requires
- A write request for {PIPE_BUF} or fewer bytes shall have the
following effect: if there is sufficient space available in the
pipe, write() shall transfer all the data and return the number
of bytes requested. Otherwise, write() shall transfer no data and
return -1 with errno set to [EAGAIN].
- A write request for more than {PIPE_BUF} bytes shall cause one
of the following:
- When at least one byte can be written, transfer what it can and
return the number of bytes written. When all data previously
written to the pipe is read, it shall transfer at least {PIPE_BUF}
bytes.
- When no data can be written, transfer no data, and return -1 with
errno set to [EAGAIN]. */
while (len1 > 0)
{
status = NtWriteFile (get_handle (), evt, NULL, NULL, &io,
(PVOID) ptr, len1, NULL, NULL);
if (evt || !NT_SUCCESS (status) || io.Information > 0
|| len <= PIPE_BUF)
break;
len1 >>= 1;
}
if (evt && status == STATUS_PENDING)
{
waitret = cygwait (evt);
@ -375,13 +401,11 @@ fhandler_pipe::raw_write (const void *ptr, size_t len)
else if (NT_SUCCESS (status))
{
nbytes_now = io.Information;
/* NtWriteFile returns success with # of bytes written == 0
if writing on a non-blocking pipe fails because the pipe
buffer doesn't have sufficient space. */
if (nbytes_now == 0)
set_errno (EAGAIN);
ptr = ((char *) ptr) + nbytes_now;
nbytes += nbytes_now;
/* 0 bytes returned? EAGAIN. See above. */
if (nbytes == 0)
set_errno (EAGAIN);
}
else if (STATUS_PIPE_IS_CLOSED (status))
{
@ -392,17 +416,16 @@ fhandler_pipe::raw_write (const void *ptr, size_t len)
__seterrno_from_nt_status (status);
if (nbytes_now == 0)
len = 0; /* Terminate loop. */
if (nbytes > 0)
ret = nbytes;
break;
}
if (evt)
CloseHandle (evt);
if (status == STATUS_THREAD_SIGNALED && ret < 0)
if (status == STATUS_THREAD_SIGNALED && nbytes == 0)
set_errno (EINTR);
else if (status == STATUS_THREAD_CANCELED)
pthread::static_cancel_self ();
return ret;
return nbytes ?: -1;
}
}
int