On Saturday 10 March 2012 23:55, Kevin Cernekee wrote:
> On Sat, Feb 12, 2011 at 6:31 PM, Denys Vlasenko
> <vda.li...@googlemail.com> wrote:
> >> >Currently, uclibc retains buffered data on stdio write errors,
> >> >and subsequent fclose and fflush will try to write it out again
> >> >(in most cases, in vain).
>
> This seems to be causing some strange problems on bash as well. Is
> there any interest in trying to mimic the glibc behavior?
>
> uClibc version is 0.9.32.1.
>
>
> bash problem:
>
> # bash --version
> GNU bash, version 3.2.0(1)-release (mipsel-unknown-linux-gnu)
> Copyright (C) 2005 Free Software Foundation, Inc.
> # echo "none of the above" > /sys/power/state
> sh: echo: write error: Invalid argument
> # aaaaa
> sh: aaaaa: command not found
> none of the abov# bbbbb
> sh: bbbbb: command not found
> none of the abov#
> # echo mem > /sys/power/state
> sh: echo: write error: Invalid argument
> # echo mem > /sys/power/state
> sh: echo: write error: Invalid argument
> # busybox echo mem > /sys/power/state
> PM: Syncing filesystems ... done.
> Freezing user space processes ... (elapsed 0.01 seconds) done.
> Freezing remaining freezable tasks ... (elapsed 0.01 seconds) done.
> Suspending console(s) (use no_console_suspend to debug)
>
>
> Simple test case to show that the buffered data persists (albeit in
> truncated form) even after calling fflush() and clearerr():
>
> -- 8< --
>
> #include <stdio.h>
> #include <unistd.h>
> #include <fcntl.h>
>
> int main(int argc, char **argv)
> {
> int tmpfd, fd;
>
> tmpfd = fcntl(fileno(stdout), F_DUPFD, 0);
> fd = open("/dev/null", O_RDONLY);
>
> dup2(fd, fileno(stdout));
>
> printf("hello world\n");
> fflush(stdout);
> if (ferror(stdout))
> clearerr(stdout);
>
> dup2(tmpfd, fileno(stdout));
>
> printf("goodbye world\n");
>
> return 0;
> }
>
> -- 8< --
>
> Output:
>
> # ./test
> hello worlgoodbye world
I propose the following patch.
Only compile tested by me, care to run-test?
--
vda
diff --git a/libc/stdio/_stdio.h b/libc/stdio/_stdio.h
index 2c0efc9..78069a5 100644
--- a/libc/stdio/_stdio.h
+++ b/libc/stdio/_stdio.h
@@ -212,7 +212,7 @@ extern int __stdio_seek(FILE *stream, register __offmax_t
*pos, int whence) attr
#define __STDIO_STREAM_SET_EOF(S) \
((void)((S)->__modeflags |= __FLAG_EOF))
#define __STDIO_STREAM_SET_ERROR(S) \
- ((void)((S)->__modeflags |= __FLAG_ERROR))
+ ((void)((S)->__errno_value = errno, (S)->__modeflags |= __FLAG_ERROR))
#define __STDIO_STREAM_CLEAR_EOF(S) \
((void)((S)->__modeflags &= ~__FLAG_EOF))
diff --git a/libc/stdio/clearerr.c b/libc/stdio/clearerr.c
index a96ecaa..af1d09f 100644
--- a/libc/stdio/clearerr.c
+++ b/libc/stdio/clearerr.c
@@ -7,6 +7,41 @@
#include "_stdio.h"
+static inline void discard_buffered_data(FILE *stream)
+{
+#ifdef __STDIO_BUFFERS
+ /* Puty, but fpurge is rather non-portable,
+ * thus many apps won't use it. Let them be able to clear
+ * buffered data on write errors using clearerr().
+ */
+ if (__FERROR_UNLOCKED(stream) /* was there indeed an error? */
+ && __STDIO_STREAM_IS_WRITING(stream)
+ && stream->__errno_value != 0
+ && stream->__errno_value != EINTR
+ && stream->__errno_value != EAGAIN
+ /* add more non-fatal error codes here */
+ ) {
+ stream->__bufpos = stream->__bufstart;
+ /*
+ * Prevent spurious buffer resets on superfluous clearerrs.
+ * Example:
+ *
+ * close(fileno(stdout));
+ * printf("Hi there!\n"); // error happens here, data is
buffered
+ * dup2(good_fd, fileno(stdout));
+ * clearerr(stdout); // drops buffered data
+ * printf("Hi there!"); // buffers new data
+ * clearerr(stdout); // must NOT drop newly buffered data
+ *
+ * We assure this by __FERROR_UNLOCKED check above,
+ * and by clearing __errno_value below
+ * (yes, I am a bit paranoid).
+ */
+ stream->__errno_value = 0;
+ }
+#endif
+}
+
#undef clearerr
#ifdef __DO_UNLOCKED
@@ -15,6 +50,8 @@ void clearerr_unlocked(register FILE *stream)
{
__STDIO_STREAM_VALIDATE(stream);
+ discard_buffered_data(stream);
+
__CLEARERR_UNLOCKED(stream);
}
@@ -32,6 +69,8 @@ void clearerr(register FILE *stream)
__STDIO_STREAM_VALIDATE(stream);
+ discard_buffered_data(stream);
+
__CLEARERR_UNLOCKED(stream);
__STDIO_AUTO_THREADUNLOCK(stream);
diff --git a/libc/stdio/fflush.c b/libc/stdio/fflush.c
index d9104a4..4599b58 100644
--- a/libc/stdio/fflush.c
+++ b/libc/stdio/fflush.c
@@ -134,8 +134,8 @@ int fflush_unlocked(register FILE *stream)
* shouldn't flush a stream you were reading from. As usual,
glibc
* caters to broken programs and simply ignores this. */
__UNDEFINED_OR_NONPORTABLE;
- __STDIO_STREAM_SET_ERROR(stream);
__set_errno(EBADF);
+ __STDIO_STREAM_SET_ERROR(stream);
retval = EOF;
}
#endif
@@ -166,8 +166,8 @@ int fflush_unlocked(register FILE *stream)
* shouldn't flush a stream you were reading from. As usual,
glibc
* caters to broken programs and simply ignores this. */
__UNDEFINED_OR_NONPORTABLE;
- __STDIO_STREAM_SET_ERROR(stream);
__set_errno(EBADF);
+ __STDIO_STREAM_SET_ERROR(stream);
return EOF;
}
#endif
diff --git a/libc/stdio/fread.c b/libc/stdio/fread.c
index d2fcc70..5ef358b 100644
--- a/libc/stdio/fread.c
+++ b/libc/stdio/fread.c
@@ -77,8 +77,8 @@ size_t fread_unlocked(void * __restrict ptr, size_t size,
size_t nmemb,
return (bytes - todo) / size;
}
- __STDIO_STREAM_SET_ERROR(stream);
__set_errno(EINVAL);
+ __STDIO_STREAM_SET_ERROR(stream);
}
__STDIO_STREAM_VALIDATE(stream);
diff --git a/libc/stdio/fwrite.c b/libc/stdio/fwrite.c
index 71793ff..3eacd7e 100644
--- a/libc/stdio/fwrite.c
+++ b/libc/stdio/fwrite.c
@@ -28,8 +28,8 @@ size_t fwrite_unlocked(const void * __restrict ptr, size_t
size,
size*nmemb,
stream) / size;
}
- __STDIO_STREAM_SET_ERROR(stream);
__set_errno(EINVAL);
+ __STDIO_STREAM_SET_ERROR(stream);
}
return 0;
diff --git a/libc/sysdeps/linux/common/bits/uClibc_stdio.h
b/libc/sysdeps/linux/common/bits/uClibc_stdio.h
index a8cf4eb..f746f14 100644
--- a/libc/sysdeps/linux/common/bits/uClibc_stdio.h
+++ b/libc/sysdeps/linux/common/bits/uClibc_stdio.h
@@ -250,6 +250,7 @@ struct __STDIO_FILE_STRUCT {
unsigned char __ungot[2];
#endif /* __UCLIBC_HAS_WCHAR__ */
int __filedes;
+ int __errno_value;
#ifdef __STDIO_BUFFERS
unsigned char *__bufstart; /* pointer to buffer */
unsigned char *__bufend; /* pointer to 1 past end of buffer */
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