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Fix GH-19570: unable to fseek in /dev/zero and /dev/null #19736
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On Linux, these two character devices are exceptions in that they can be seeked. Check their major/minor device number.
devnexen
devnexen
reviewed
Sep 6, 2025
@@ -255,7 +259,18 @@ PHPAPI php_stream *_php_stream_fopen_tmpfile(int dummy STREAMS_DC)
static void detect_is_seekable(php_stdio_stream_data *self) {
#if defined(S_ISFIFO) && defined(S_ISCHR)
if (self->fd >= 0 && do_fstat(self, 0) == 0) {
#ifdef __linux__
if (S_ISCHR(self->sb.st_mode)) {
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note that not just linux, allows some character devices being seekable, e.g. freebsd and very likely macos. The equivalent for freebsd at least, can t rely on device versions at all but on a "poorer" solution such as if fseek returns -1 and errno is ESPIPE then it is not seekable.
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On Linux, these two character devices are exceptions in that they can be seeked. Check their major/minor device number.