[PATCH] Cygwin: pipe: Switch pipe mode to blocking mode by defaut
Takashi Yano
takashi.yano@nifty.ne.jp
Thu Sep 5 13:18:31 GMT 2024
Previously, cygwin read pipe used non-blocking mode althogh non-
cygwin app uses blocking-mode by default. Despite this requirement,
if a cygwin app is executed from a non-cygwwin app and the cygwin
app exits, read pipe remains on non-blocking mode because of the
commit fc691d0246b9. Due to this behaviour, the non-cygwin app
cannot read the pipe correctly after that. Similarly, if a non-
cygwin app is executed from a cygwin app and the non-cygwin app
exits, the read pipe mode remains on blocking mode although cygwin
read pipe should be non-blocking mode.
These bugs were provoked by pipe mode toggling between cygwin and
non-cygwin apps. To make management of pipe mode simpler,
This patch has re-designed the pipe implementation. In this new
implementation, both read and wrie pipe basically use only blocking
mode and the behaviour corresponding to the pipe mode is simulated
in raw_read() and raw_wrie(). Only when the query handle is not
available, the raw_write() cannot simulate non-blocking access.
Therefore, the pipe mode is temporarily changed to non-blocking
mode. This happens only if the pipe is created by non-cygwin app
and cygwin inherits that.
Addresses: https://github.com/git-for-windows/git/issues/5115
Fixes: fc691d0246b9 ("Cygwin: pipe: Make sure to set read pipe non-blocking for cygwin apps.");
Reported-by: isaacag, Johannes Schindelin <Johannes.Schindelin@gmx.de>
Reviewed-by:
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
---
winsup/cygwin/dtable.cc | 5 +-
winsup/cygwin/fhandler/pipe.cc | 352 ++++++++++--------------
winsup/cygwin/local_includes/fhandler.h | 4 +-
winsup/cygwin/select.cc | 19 +-
4 files changed, 157 insertions(+), 223 deletions(-)
diff --git a/winsup/cygwin/dtable.cc b/winsup/cygwin/dtable.cc
index 9508f3e0b..7303f7eac 100644
--- a/winsup/cygwin/dtable.cc
+++ b/winsup/cygwin/dtable.cc
@@ -410,9 +410,8 @@ dtable::init_std_file_from_handle (int fd, HANDLE handle)
{
fhandler_pipe *fhp = (fhandler_pipe *) fh;
fhp->set_pipe_buf_size ();
- /* Set read pipe always to nonblocking */
- fhp->set_pipe_non_blocking (fhp->get_device () == FH_PIPER ?
- true : fhp->is_nonblocking ());
+ /* Set pipe always blocking */
+ fhp->set_pipe_non_blocking (false);
}
if (!fh->open_setup (openflags))
diff --git a/winsup/cygwin/fhandler/pipe.cc b/winsup/cygwin/fhandler/pipe.cc
index c686df650..942de82b2 100644
--- a/winsup/cygwin/fhandler/pipe.cc
+++ b/winsup/cygwin/fhandler/pipe.cc
@@ -48,7 +48,7 @@ fhandler_pipe::fhandler_pipe ()
In addition to setting the blocking mode of the pipe handle, it
also sets the pipe's read mode to byte_stream unconditionally. */
-void
+bool
fhandler_pipe::set_pipe_non_blocking (bool nonblocking)
{
NTSTATUS status;
@@ -62,6 +62,7 @@ fhandler_pipe::set_pipe_non_blocking (bool nonblocking)
FilePipeInformation);
if (!NT_SUCCESS (status))
debug_printf ("NtSetInformationFile(FilePipeInformation): %y", status);
+ return NT_SUCCESS (status);
}
int
@@ -91,10 +92,10 @@ fhandler_pipe::init (HANDLE f, DWORD a, mode_t mode, int64_t uniq_id)
set_ino (uniq_id);
set_unique_id (uniq_id | !!(mode & GENERIC_WRITE));
if (opened_properly)
- /* Set read pipe always nonblocking to allow signal handling
- even with FILE_SYNCHRONOUS_IO_NONALERT. */
- set_pipe_non_blocking (get_device () == FH_PIPER ?
- true : is_nonblocking ());
+ /* Set pipe always blocking and simulate non-blocking mode in
+ raw_read()/raw_write() to allow signal handling even with
+ FILE_SYNCHRONOUS_IO_NONALERT. */
+ set_pipe_non_blocking (false);
/* Store pipe name to path_conv pc for query_hdl check */
if (get_dev () == FH_PIPEW)
@@ -333,17 +334,42 @@ fhandler_pipe::raw_read (void *ptr, size_t& len)
ULONG len1 = (ULONG) (len - nbytes);
DWORD select_sem_timeout = 0;
- FILE_PIPE_LOCAL_INFORMATION fpli;
- status = NtQueryInformationFile (get_handle (), &io,
- &fpli, sizeof (fpli),
- FilePipeLocalInformation);
- if (NT_SUCCESS (status))
+ DWORD n;
+ BOOL ret = PeekNamedPipe (get_handle (), NULL, 0, NULL, &n, NULL);
+ if (!ret) /* Broken pipe ? */
+ break;
+ if (n == 0)
{
- if (fpli.ReadDataAvailable == 0 && nbytes != 0)
+ if (nbytes != 0)
break;
+ if (is_nonblocking ())
+ {
+ set_errno (EAGAIN);
+ nbytes = (size_t) -1;
+ break;
+ }
+ /* If the pipe is a non-cygwin pipe, select_sem trick
+ does not work. As a result, the following cygwait()
+ will return only after timeout occurs. This causes
+ performance degradation. However, setting timeout
+ to zero causes high CPU load. So, set timeout to
+ non-zero only when select_sem is valid or pipe is
+ not ready to read for more than t0_threshold.
+ This prevents both the performance degradation and
+ the high CPU load. */
+ if (select_sem || GetTickCount64 () - t0 > t0_threshold)
+ select_sem_timeout = 1;
+ waitret = cygwait (select_sem, select_sem_timeout);
+ if (waitret == WAIT_CANCELED)
+ pthread::static_cancel_self ();
+ else if (waitret == WAIT_SIGNALED)
+ {
+ set_errno (EINTR);
+ nbytes = (size_t) -1;
+ break;
+ }
+ continue;
}
- else if (nbytes != 0)
- break;
status = NtReadFile (get_handle (), NULL, NULL, NULL, &io, ptr,
len1, NULL, NULL);
if (isclosed ()) /* A signal handler might have closed the fd. */
@@ -368,37 +394,6 @@ fhandler_pipe::raw_read (void *ptr, size_t& len)
case STATUS_PIPE_BROKEN:
/* This is really EOF. */
break;
- case STATUS_PIPE_LISTENING:
- case STATUS_PIPE_EMPTY:
- if (nbytes != 0)
- break;
- if (is_nonblocking ())
- {
- set_errno (EAGAIN);
- nbytes = (size_t) -1;
- break;
- }
- /* If the pipe is a non-cygwin pipe, select_sem trick
- does not work. As a result, the following cygwait()
- will return only after timeout occurs. This causes
- performance degradation. However, setting timeout
- to zero causes high CPU load. So, set timeout to
- non-zero only when select_sem is valid or pipe is
- not ready to read for more than t0_threshold.
- This prevents both the performance degradation and
- the high CPU load. */
- if (select_sem || GetTickCount64 () - t0 > t0_threshold)
- select_sem_timeout = 1;
- waitret = cygwait (select_sem, select_sem_timeout);
- if (waitret == WAIT_CANCELED)
- pthread::static_cancel_self ();
- else if (waitret == WAIT_SIGNALED)
- {
- set_errno (EINTR);
- nbytes = (size_t) -1;
- break;
- }
- continue;
default:
__seterrno_from_nt_status (status);
nbytes = (size_t) -1;
@@ -446,12 +441,20 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
return -1;
}
- if (len <= pipe_buf_size || pipe_buf_size == 0)
+ bool query_hdl_available = true;
+ ssize_t avail = pipe_buf_size;
+ if (is_nonblocking ())
+ avail = pipe_data_available (-1, this, get_handle (), PDA_WRITE);
+ if (avail == 0)
+ {
+ set_errno (EAGAIN);
+ return -1;
+ }
+
+ if (len <= (size_t) avail || pipe_buf_size == 0)
chunk = len;
- else if (is_nonblocking ())
- chunk = len = pipe_buf_size;
else
- chunk = pipe_buf_size;
+ chunk = avail;
if (!(evt = CreateEvent (NULL, false, false, NULL)))
{
@@ -459,6 +462,28 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
return -1;
}
+ if (is_nonblocking ())
+ {
+ fhandler_pipe *fh = (fhandler_pipe *) this;
+ query_hdl_available =
+ fh->get_query_handle () || fh->temporary_query_hdl ();
+ if (avail > 1 || query_hdl_available)
+ len = chunk;
+ else if (avail == 0) /* The pipe is really full. */
+ {
+ set_errno (EAGAIN);
+ return -1;
+ }
+ else if (!fh->set_pipe_non_blocking (true))
+ /* NtSetInformationFile() in set_pipe_non_blocking(true)
+ fails for unknown reasons if the pipe is not empty.
+ In this case, no pipe reader should be reading the pipe,
+ so pipe_data_available() has returned correct value. */
+ len = chunk; /* The pipe is not empty. */
+ else
+ chunk = len = min (len, pipe_buf_size); /* The pipe is empty. */
+ }
+
/* Write in chunks, accumulating a total. If there's an error, just
return the accumulated total unless the first write fails, in
which case return -1. */
@@ -528,6 +553,12 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
waitret = WAIT_SIGNALED;
break;
}
+ if (waitret == WAIT_TIMEOUT && is_nonblocking ())
+ {
+ CancelIo (get_handle ());
+ set_errno (EAGAIN);
+ goto out;
+ }
cygwait (select_sem, 10, cw_cancel);
}
/* Loop in case of blocking write or SA_RESTART */
@@ -610,6 +641,9 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t len)
break;
}
out:
+ if (avail == 1 && !query_hdl_available)
+ ((fhandler_pipe *) this)->set_pipe_non_blocking (false);
+
CloseHandle (evt);
if (status == STATUS_THREAD_SIGNALED && nbytes == 0)
set_errno (EINTR);
@@ -649,17 +683,6 @@ fhandler_pipe::fixup_after_fork (HANDLE parent)
ReleaseMutex (hdl_cnt_mtx);
}
-void
-fhandler_pipe::fixup_after_exec ()
-{
- /* Set read pipe itself always non-blocking for cygwin process.
- Blocking/non-blocking is simulated in raw_read(). For write
- pipe, follow is_nonblocking(). */
- bool mode = get_device () == FH_PIPEW ? is_nonblocking () : true;
- set_pipe_non_blocking (mode);
- fhandler_base::fixup_after_exec ();
-}
-
int
fhandler_pipe::dup (fhandler_base *child, int flags)
{
@@ -745,6 +768,7 @@ fhandler_pipe::close ()
}
#define PIPE_INTRO "\\\\.\\pipe\\cygwin-"
+#define PIPE_INTRO_NT "\\\\.\\pipe\\"
/* Create a pipe, and return handles to the read and write ends,
just like CreatePipe, but ensure that the write end permits
@@ -769,8 +793,16 @@ fhandler_pipe::create (LPSECURITY_ATTRIBUTES sa_ptr, PHANDLE r, PHANDLE w,
psize = DEFAULT_PIPEBUFSIZE;
char pipename[MAX_PATH];
- size_t len = __small_sprintf (pipename, PIPE_INTRO "%S-",
- &cygheap->installation_key);
+ size_t len = __small_sprintf(pipename, "%S-%u-pipe-nt-0x",
+ &cygheap->installation_key,
+ GetCurrentProcessId ());
+ bool nt = !strncmp (name, pipename, len);
+ if (nt)
+ len = __small_sprintf (pipename, PIPE_INTRO_NT "%S-",
+ &cygheap->installation_key);
+ else
+ len = __small_sprintf (pipename, PIPE_INTRO "%S-",
+ &cygheap->installation_key);
DWORD pipe_mode = PIPE_READMODE_BYTE | PIPE_REJECT_REMOTE_CLIENTS;
if (!name)
pipe_mode |= pipe_byte ? PIPE_TYPE_BYTE : PIPE_TYPE_MESSAGE;
@@ -821,11 +853,27 @@ fhandler_pipe::create (LPSECURITY_ATTRIBUTES sa_ptr, PHANDLE r, PHANDLE w,
definitely required for pty handling since fhandler_pty_master
writes to the pipe in chunks, terminated by newline when CANON mode
is specified. */
- *r = CreateNamedPipe (pipename, open_mode, pipe_mode, 1, psize,
- psize, NMPWAIT_USE_DEFAULT_WAIT, sa_ptr);
+ /* PIPE_ACCESS_OUTBOUND is added to acquire FILE_WRITE_ATTRIBUTES right.
+ Unnecessary rights such as FILE_WRITE_DATA will be dropped later. */
+ *r = CreateNamedPipe (pipename, open_mode | PIPE_ACCESS_OUTBOUND,
+ pipe_mode, 1, psize, psize,
+ NMPWAIT_USE_DEFAULT_WAIT, sa_ptr);
if (*r != INVALID_HANDLE_VALUE)
{
+ /* Drop unnecessary access rights. */
+ HANDLE rtmp;
+ DWORD access = GENERIC_READ | FILE_WRITE_ATTRIBUTES;
+ if (nt)
+ /* Add this right as a marker of cygwin read pipe for query_hdl */
+ access |= FILE_WRITE_EA;
+ if (DuplicateHandle (GetCurrentProcess (), r,
+ GetCurrentProcess (), &rtmp,
+ access, sa_ptr->bInheritHandle, 0))
+ {
+ CloseHandle (*r);
+ *r = rtmp;
+ }
debug_printf ("pipe read handle %p", *r);
err = 0;
break;
@@ -916,6 +964,11 @@ is_running_as_service (void)
simplicity, nt_create will omit the 'open_mode' and 'name'
parameters, which aren't needed for our purposes. */
+/* Regardless of above comment, the current nt_create() is reverted to just
+ call fhandler_pipe::create() to allow adding FILE_FLAG_OVERLAPPED flag.
+ This is needed for query_hdl so that PeekNamedPipe() and NtQueryObject()
+ are not blocked even while reader is reading the pipe. */
+
static int nt_create (LPSECURITY_ATTRIBUTES, HANDLE &, HANDLE &, DWORD,
int64_t *);
@@ -955,8 +1008,7 @@ fhandler_pipe::create (fhandler_pipe *fhs[2], unsigned psize, int mode)
0, sa->bInheritHandle, DUPLICATE_SAME_ACCESS))
goto err_close_select_sem0;
- if (is_running_as_service () &&
- !DuplicateHandle (GetCurrentProcess (), r,
+ if (!DuplicateHandle (GetCurrentProcess (), r,
GetCurrentProcess (), &fhs[1]->query_hdl,
FILE_READ_DATA, sa->bInheritHandle, 0))
goto err_close_select_sem1;
@@ -1005,131 +1057,29 @@ out:
return res;
}
+/* Current nt_create() does not use NtCreateNamedPipe() at all. The
+ function name is just inherited from previous implementation of
+ fhandler_pipe. */
static int
nt_create (LPSECURITY_ATTRIBUTES sa_ptr, HANDLE &r, HANDLE &w,
DWORD psize, int64_t *unique_id)
{
- NTSTATUS status;
- HANDLE npfsh;
- ACCESS_MASK access;
- OBJECT_ATTRIBUTES attr;
- IO_STATUS_BLOCK io;
- LARGE_INTEGER timeout;
-
- /* Default to error. */
- r = NULL;
- w = NULL;
-
- status = fhandler_base::npfs_handle (npfsh);
- if (!NT_SUCCESS (status))
- {
- __seterrno_from_nt_status (status);
- return GetLastError ();
- }
-
- /* Ensure that there is enough pipe buffer space for atomic writes. */
- if (!psize)
- psize = DEFAULT_PIPEBUFSIZE;
-
- UNICODE_STRING pipename;
- WCHAR pipename_buf[MAX_PATH];
- size_t len = __small_swprintf (pipename_buf, L"%S-%u-",
- &cygheap->installation_key,
- GetCurrentProcessId ());
-
- access = GENERIC_READ | FILE_WRITE_ATTRIBUTES | SYNCHRONIZE;
- access |= FILE_WRITE_EA; /* Add this right as a marker of cygwin read pipe */
-
- ULONG pipe_type = pipe_byte ? FILE_PIPE_BYTE_STREAM_TYPE
- : FILE_PIPE_MESSAGE_TYPE;
-
- /* Retry NtCreateNamedPipeFile as long as the pipe name is in use.
- Retrying will probably never be necessary, but we want
- to be as robust as possible. */
- DWORD err = 0;
- while (!r)
- {
- static volatile ULONG pipe_unique_id;
- LONG id = InterlockedIncrement ((LONG *) &pipe_unique_id);
- __small_swprintf (pipename_buf + len, L"pipe-nt-%p", id);
- if (unique_id)
- *unique_id = ((int64_t) id << 32 | GetCurrentProcessId ());
-
- debug_printf ("name %W, size %u, mode %s", pipename_buf, psize,
- (pipe_type & FILE_PIPE_MESSAGE_TYPE)
- ? "PIPE_TYPE_MESSAGE" : "PIPE_TYPE_BYTE");
-
- RtlInitUnicodeString (&pipename, pipename_buf);
-
- InitializeObjectAttributes (&attr, &pipename,
- sa_ptr->bInheritHandle ? OBJ_INHERIT : 0,
- npfsh, sa_ptr->lpSecurityDescriptor);
-
- timeout.QuadPart = -500000;
- /* Set FILE_SYNCHRONOUS_IO_NONALERT flag so that native
- C# programs work with cygwin pipe. */
- status = NtCreateNamedPipeFile (&r, access, &attr, &io,
- FILE_SHARE_READ | FILE_SHARE_WRITE,
- FILE_CREATE,
- FILE_SYNCHRONOUS_IO_NONALERT, pipe_type,
- FILE_PIPE_BYTE_STREAM_MODE,
- 0, 1, psize, psize, &timeout);
-
- if (NT_SUCCESS (status))
- {
- debug_printf ("pipe read handle %p", r);
- err = 0;
- break;
- }
-
- switch (status)
- {
- case STATUS_PIPE_BUSY:
- case STATUS_INSTANCE_NOT_AVAILABLE:
- case STATUS_PIPE_NOT_AVAILABLE:
- /* The pipe is already open with compatible parameters.
- Pick a new name and retry. */
- debug_printf ("pipe busy, retrying");
- r = NULL;
- break;
- case STATUS_ACCESS_DENIED:
- /* The pipe is already open with incompatible parameters.
- Pick a new name and retry. */
- debug_printf ("pipe access denied, retrying");
- r = NULL;
- break;
- default:
- {
- __seterrno_from_nt_status (status);
- err = GetLastError ();
- debug_printf ("failed, %E");
- r = NULL;
- }
- }
- }
-
- if (err)
- {
- r = NULL;
- return err;
- }
-
- debug_printf ("NtOpenFile: name %S", &pipename);
-
- access = GENERIC_WRITE | FILE_READ_ATTRIBUTES | SYNCHRONIZE;
- status = NtOpenFile (&w, access, &attr, &io, 0, 0);
- if (!NT_SUCCESS (status))
- {
- DWORD err = GetLastError ();
- debug_printf ("NtOpenFile failed, r %p, %E", r);
- if (r)
- NtClose (r);
- w = NULL;
- return err;
- }
-
- /* Success. */
- return 0;
+ char name[MAX_PATH];
+ size_t len = __small_sprintf (name, "%u-", GetCurrentProcessId ());
+ static volatile ULONG pipe_unique_id;
+ LONG id = InterlockedIncrement ((LONG *) &pipe_unique_id);
+ __small_sprintf (name + len, "pipe-nt-%p", id);
+ *unique_id = ((int64_t) id << 32 | GetCurrentProcessId ());
+
+ /* FILE_FLAG_OVERLAPPED is added here to allow PeekNamedPipe() and
+ NtQueryObject() be not blocked even while reader is reading the
+ pipe.
+ Accordig to the official document, to access the handle opened
+ with FILE_FLAG_OVERLAPPED, it is mandatory to pass the OVERLAPPED
+ structure. However, in fact, it seems that the access will fallback
+ to the blocking access if it is not specified. */
+ return fhandler_pipe::create (sa_ptr, &r, &w, psize, name,
+ FILE_FLAG_OVERLAPPED, unique_id);
}
/* Called by dtable::init_std_file_from_handle for stdio handles
@@ -1174,22 +1124,6 @@ fhandler_pipe::ioctl (unsigned int cmd, void *p)
return 0;
}
-int
-fhandler_pipe::fcntl (int cmd, intptr_t arg)
-{
- if (cmd != F_SETFL)
- return fhandler_base::fcntl (cmd, arg);
-
- const bool was_nonblocking = is_nonblocking ();
- int res = fhandler_base::fcntl (cmd, arg);
- const bool now_nonblocking = is_nonblocking ();
- /* Do not set blocking mode for read pipe to allow signal handling
- even with FILE_SYNCHRONOUS_IO_NONALERT. */
- if (now_nonblocking != was_nonblocking && get_device () != FH_PIPER)
- set_pipe_non_blocking (now_nonblocking);
- return res;
-}
-
int
fhandler_pipe::fstat (struct stat *buf)
{
@@ -1262,11 +1196,8 @@ fhandler_pipe::get_query_hdl_per_process (OBJECT_NAME_INFORMATION *ntfn)
NTSTATUS status;
ULONG len;
- /* Non-cygwin app may call ReadFile() for empty pipe, which makes
- NtQueryObject() for ObjectNameInformation block. Therefore, do
- not try to get query_hdl for non-cygwin apps. */
_pinfo *p = pids[i];
- if (!p || ISSTATE (p, PID_NOTCYGWIN))
+ if (!p)
continue;
HANDLE proc = OpenProcess (PROCESS_DUP_HANDLE
@@ -1361,18 +1292,11 @@ fhandler_pipe::spawn_worker (int fileno_stdin, int fileno_stdout,
if (cfd->get_dev () == FH_PIPEW
&& (fd == fileno_stdout || fd == fileno_stderr))
{
+ /* Setup for query_hdl stuff. Read the comment below. */
fhandler_pipe *pipe = (fhandler_pipe *)(fhandler_base *) cfd;
- pipe->set_pipe_non_blocking (false);
-
- /* Setup for query_ndl stuff. Read the comment below. */
if (pipe->request_close_query_hdl ())
need_send_noncygchld_sig = true;
}
- else if (cfd->get_dev () == FH_PIPER && fd == fileno_stdin)
- {
- fhandler_pipe *pipe = (fhandler_pipe *)(fhandler_base *) cfd;
- pipe->set_pipe_non_blocking (false);
- }
/* If multiple writers including non-cygwin app exist, the non-cygwin
app cannot detect pipe closure on the read side when the pipe is
diff --git a/winsup/cygwin/local_includes/fhandler.h b/winsup/cygwin/local_includes/fhandler.h
index 1c339cfbc..a6281d0c0 100644
--- a/winsup/cygwin/local_includes/fhandler.h
+++ b/winsup/cygwin/local_includes/fhandler.h
@@ -1234,13 +1234,11 @@ public:
int open (int flags, mode_t mode = 0);
bool open_setup (int flags);
void fixup_after_fork (HANDLE);
- void fixup_after_exec ();
int dup (fhandler_base *child, int);
void set_close_on_exec (bool val);
int close ();
void raw_read (void *ptr, size_t& len);
int ioctl (unsigned int cmd, void *);
- int fcntl (int cmd, intptr_t);
int fstat (struct stat *buf);
int fstatvfs (struct statvfs *buf);
int fadvise (off_t, off_t, int);
@@ -1265,7 +1263,7 @@ public:
fh->copy_from (this);
return fh;
}
- void set_pipe_non_blocking (bool nonblocking);
+ bool set_pipe_non_blocking (bool nonblocking);
HANDLE get_query_handle () const { return query_hdl; }
void close_query_handle ()
{
diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index bc02c3f9d..672e856ef 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -642,7 +642,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, int flags)
Consequentially, the only reliable information is available on the
read side, so fetch info from the read side via the pipe-specific
query handle. Use fpli.WriteQuotaAvailable as storage for the actual
- interesting value, which is the InboundQuote on the write side,
+ interesting value, which is the OutboundQuota on the write side,
decremented by the number of bytes of data in that buffer. */
/* Note: Do not use NtQueryInformationFile() for query_hdl because
NtQueryInformationFile() seems to interfere with reading pipes
@@ -659,7 +659,20 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, int flags)
if (!query_hdl)
query_hdl = ((fhandler_pipe *) fh)->temporary_query_hdl ();
if (!query_hdl) /* We cannot know actual write pipe space. */
- return (flags & PDA_SELECT) ? PIPE_BUF : 1;
+ {
+ /* NtSetInformationFile() in set_pipe_non_blocking(true)
+ fails for unknown reasons if the pipe is not empty.
+ In this case, no pipe reader should be reading the pipe,
+ so the pipe is really full if WriteQuotaAvailable
+ is zero.*/
+ if (!((fhandler_pipe *) fh)->set_pipe_non_blocking (true))
+ return 0;
+ /* Restore pipe mode to blocking mode */
+ ((fhandler_pipe *) fh)->set_pipe_non_blocking (false);
+ /* The pipe is empty here because set_pipe_non_blocking(true)
+ has succeeded. */
+ return fpli.OutboundQuota;;
+ }
DWORD nbytes_in_pipe;
BOOL res =
PeekNamedPipe (query_hdl, NULL, 0, NULL, &nbytes_in_pipe, NULL);
@@ -667,7 +680,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h, int flags)
CloseHandle (query_hdl); /* Close temporary query_hdl */
if (!res) /* We cannot know actual write pipe space. */
return (flags & PDA_SELECT) ? PIPE_BUF : 1;
- fpli.WriteQuotaAvailable = fpli.InboundQuota - nbytes_in_pipe;
+ fpli.WriteQuotaAvailable = fpli.OutboundQuota - nbytes_in_pipe;
}
if (fpli.WriteQuotaAvailable > 0)
{
--
2.45.1
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