https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=6d6af651151d48796204d4a358db8ef3c121a501
commit 6d6af651151d48796204d4a358db8ef3c121a501
Author: Takashi Yano <takashi.y...@nifty.ne.jp>
Date: Fri Jun 27 20:23:11 2025 +0900
Cygwin: pipe: Make pipe_data_available() return PDA_UNKNOWN
... rather than 1 when the pipe space estimation fails, so that
select() and raw_wrie() can perform appropriate fallback handling.
In select(), even if pipe space is unknown, return writable to avoid
deadlock. Even with select() returns writable, write() can blocked
anyway, if data is larger than pipe space. In raw_write(), if the
pipe is real non-blocking mode, attempting to write larger data than
pipe space is safe. Otherwise, return error.
For other cases than FH_PIPEW, PDA_UNKNOWN never orrurs. Therefore,
it is not necessary to handle it in that cases.
Reviewed-by: Johannes Schindelin <johannes.schinde...@gmx.de>
Signed-off-by: Takashi Yano <takashi.y...@nifty.ne.jp>
Diff:
---
winsup/cygwin/fhandler/pipe.cc | 7 ++++---
winsup/cygwin/local_includes/select.h | 3 +++
winsup/cygwin/select.cc | 18 +++++++++---------
3 files changed, 16 insertions(+), 12 deletions(-)
diff --git a/winsup/cygwin/fhandler/pipe.cc b/winsup/cygwin/fhandler/pipe.cc
index 22addbb18..7e2c1861b 100644
--- a/winsup/cygwin/fhandler/pipe.cc
+++ b/winsup/cygwin/fhandler/pipe.cc
@@ -663,12 +663,13 @@ fhandler_pipe_fifo::raw_write (const void *ptr, size_t
len)
in a very implementation-defined way we can't emulate, but it
resembles it closely enough to get useful results. */
avail = pipe_data_available (-1, this, get_handle (), PDA_WRITE);
- if (avail < 1) /* error or pipe closed */
+ if (avail == PDA_UNKNOWN && real_non_blocking_mode)
+ avail = len1;
+ else if (avail == 0 || !PDA_NOERROR (avail))
+ /* error or pipe closed */
break;
if (avail > len1) /* somebody read from the pipe */
avail = len1;
- if (avail == 1) /* 1 byte left or non-Cygwin pipe */
- len1 >>= 1;
else if (avail >= PIPE_BUF)
len1 = avail & ~(PIPE_BUF - 1);
else
diff --git a/winsup/cygwin/local_includes/select.h
b/winsup/cygwin/local_includes/select.h
index 43ceb1d7e..afc05e186 100644
--- a/winsup/cygwin/local_includes/select.h
+++ b/winsup/cygwin/local_includes/select.h
@@ -143,5 +143,8 @@ ssize_t pipe_data_available (int, fhandler_base *, HANDLE,
int);
#define PDA_READ 0x00
#define PDA_WRITE 0x01
+#define PDA_ERROR -1
+#define PDA_UNKNOWN -2
+#define PDA_NOERROR(x) (x >= 0)
#endif /* _SELECT_H_ */
diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index 701f4d9a6..050221a9f 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -601,7 +601,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h,
int mode)
if (mode == PDA_READ
&& PeekNamedPipe (h, NULL, 0, NULL, &nbytes_in_pipe, NULL))
return nbytes_in_pipe;
- return -1;
+ return PDA_ERROR;
}
IO_STATUS_BLOCK iosb = {{0}, 0};
@@ -618,7 +618,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h,
int mode)
access on the write end. */
select_printf ("fd %d, %s, NtQueryInformationFile failed, status %y",
fd, fh->get_name (), status);
- return (mode == PDA_WRITE) ? 1 : -1;
+ return (mode == PDA_WRITE) ? PDA_UNKNOWN : PDA_ERROR;
}
if (mode == PDA_WRITE)
{
@@ -660,7 +660,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h,
int mode)
return fpli.WriteQuotaAvailable; /* Not empty */
else if (!NT_SUCCESS (status))
/* We cannot know actual write pipe space. */
- return 1;
+ return PDA_UNKNOWN;
/* Restore pipe mode to blocking mode */
((fhandler_pipe *) fh)->set_pipe_non_blocking (false);
/* Empty */
@@ -684,7 +684,7 @@ pipe_data_available (int fd, fhandler_base *fh, HANDLE h,
int mode)
return fpli.ReadDataAvailable;
}
if (fpli.NamedPipeState & FILE_PIPE_CLOSING_STATE)
- return -1;
+ return PDA_ERROR;
return 0;
}
@@ -734,7 +734,7 @@ peek_pipe (select_record *s, bool from_select)
if (n == 0 && fh->get_echo_handle ())
n = pipe_data_available (s->fd, fh, fh->get_echo_handle (), PDA_READ);
- if (n < 0)
+ if (n == PDA_ERROR)
{
select_printf ("read: %s, n %d", fh->get_name (), n);
if (s->except_selected)
@@ -775,8 +775,8 @@ out:
}
ssize_t n = pipe_data_available (s->fd, fh, h, PDA_WRITE);
select_printf ("write: %s, n %d", fh->get_name (), n);
- gotone += s->write_ready = (n > 0);
- if (n < 0 && s->except_selected)
+ gotone += s->write_ready = (n > 0 || n == PDA_UNKNOWN);
+ if (n == PDA_ERROR && s->except_selected)
gotone += s->except_ready = true;
}
return gotone;
@@ -989,7 +989,7 @@ out:
ssize_t n = pipe_data_available (s->fd, fh, fh->get_handle (),
PDA_WRITE);
select_printf ("write: %s, n %d", fh->get_name (), n);
gotone += s->write_ready = (n > 0);
- if (n < 0 && s->except_selected)
+ if (n == PDA_ERROR && s->except_selected)
gotone += s->except_ready = true;
}
return gotone;
@@ -1415,7 +1415,7 @@ out:
ssize_t n = pipe_data_available (s->fd, fh, h, PDA_WRITE);
select_printf ("write: %s, n %d", fh->get_name (), n);
gotone += s->write_ready = (n > 0);
- if (n < 0 && s->except_selected)
+ if (n == PDA_ERROR && s->except_selected)
gotone += s->except_ready = true;
}
return gotone;
