aboutsummaryrefslogtreecommitdiff
path: root/NEWS
diff options
context:
space:
mode:
authorZack Weinberg <zackw@panix.com>2018-02-21 19:12:51 -0500
committerZack Weinberg <zackw@panix.com>2018-03-13 08:31:56 -0400
commit2cc7bad0ae0a412e75270be5ed41d45c03e7a931 (patch)
treea726dff1dc98e5fabf47685d10f9c681265db95b /NEWS
parent778f1974863d63e858b6d0105e41d6f0c30732d3 (diff)
downloadglibc-2cc7bad0ae0a412e75270be5ed41d45c03e7a931.zip
glibc-2cc7bad0ae0a412e75270be5ed41d45c03e7a931.tar.gz
glibc-2cc7bad0ae0a412e75270be5ed41d45c03e7a931.tar.bz2
[BZ 1190] Make EOF sticky in stdio.
C99 specifies that the EOF condition on a file is "sticky": once EOF has been encountered, all subsequent reads should continue to return EOF until the file is closed or something clears the "end-of-file indicator" (e.g. fseek, clearerr). This is arguably a change from C89, where the wording was ambiguous; the BSDs always had sticky EOF, but the System V lineage would attempt to read from the underlying fd again. GNU libc has followed System V for as long as we've been using libio, but nowadays C99 conformance and BSD compatibility are more important than System V compatibility. You might wonder if changing the _underflow impls is sufficient to apply the C99 semantics to all of the many stdio functions that perform input. It should be enough to cover all paths to _IO_SYSREAD, and the only other functions that call _IO_SYSREAD are the _seekoff impls, which is OK because seeking clears EOF, and the _xsgetn impls, which, as far as I can tell, are unused within glibc. The test programs in this patch use a pseudoterminal to set up the necessary conditions. To facilitate this I added a new test-support function that sets up a pair of pty file descriptors for you; it's almost the same as BSD openpty, the only differences are that it allocates the optionally-returned tty pathname with malloc, and that it crashes if anything goes wrong. [BZ #1190] [BZ #19476] * libio/fileops.c (_IO_new_file_underflow): Return EOF immediately if the _IO_EOF_SEEN bit is already set; update commentary. * libio/oldfileops.c (_IO_old_file_underflow): Likewise. * libio/wfileops.c (_IO_wfile_underflow): Likewise. * support/support_openpty.c, support/tty.h: New files. * support/Makefile (libsupport-routines): Add support_openpty. * libio/tst-fgetc-after-eof.c, wcsmbs/test-fgetwc-after-eof.c: New test cases. * libio/Makefile (tests): Add tst-fgetc-after-eof. * wcsmbs/Makefile (tests): Add tst-fgetwc-after-eof.
Diffstat (limited to 'NEWS')
-rw-r--r--NEWS8
1 files changed, 8 insertions, 0 deletions
diff --git a/NEWS b/NEWS
index 60dd2f7..03330d4 100644
--- a/NEWS
+++ b/NEWS
@@ -28,6 +28,14 @@ Deprecated and removed features, and other changes affecting compatibility:
investigate using (f)getc_unlocked and (f)putc_unlocked, and, if
necessary, flockfile and funlockfile.
+ * All stdio functions now treat end-of-file as a sticky condition. If you
+ read from a file until EOF, and then the file is enlarged by another
+ process, you must call clearerr or another function with the same effect
+ (e.g. fseek, rewind) before you can read the additional data. This
+ corrects a longstanding C99 conformance bug. It is most likely to affect
+ programs that use stdio to read interactive input from a terminal.
+ (Bug #1190.)
+
* The macros 'major', 'minor', and 'makedev' are now only available from
the header <sys/sysmacros.h>; not from <sys/types.h> or various other
headers that happen to include <sys/types.h>. These macros are rarely