This is an extension of commit 6cb2d8c1ce77 ("Allow select() calls on FDs
that are already ready"). There, we were dealing with reads. The same
problem happens with writes.
Now, reads or writes will be detected, given that the underlying device
reports DMREADABLE/DMWRITABLE in its stat message.
Signed-off-by: Barret Rhoden <[email protected]>
---
user/iplib/select.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)
diff --git a/user/iplib/select.c b/user/iplib/select.c
index 7fc22b5cd706..557c07bd61de 100644
--- a/user/iplib/select.c
+++ b/user/iplib/select.c
@@ -59,6 +59,7 @@
#include <stdlib.h>
#include <errno.h>
#include <signal.h>
+#include <ros/fs.h>
static int epoll_fd;
static fd_set all_fds;
@@ -131,19 +132,26 @@ static int select_tv_to_ep_timeout(struct timeval *tv)
return tv->tv_sec * 1000 + DIV_ROUND_UP(tv->tv_usec, 1000);
}
-/* Check with the kernel if FD is readable or not. Some apps will call
select()
- * on something even if it is already readable.
+/* Check with the kernel if FD is readable/writable or not. Some apps will
call
+ * select() on something even if it is already actionable, and not wait until
+ * they get the EAGAIN.
*
* TODO: this *won't* work for disk based files. It only works on qids that
are
- * backed with qio queues or something similar, where size == readable. */
-static bool fd_is_readable(int fd)
+ * backed with qio queues or something similar, where the device has support
for
+ * setting DMREADABLE/DMWRITABLE. */
+static bool fd_is_actionable(int fd, fd_set *readfds, fd_set *writefds)
{
struct stat stat_buf;
int ret;
+ /* Avoid the stat call on FDs we're not tracking (which should trigger
an
+ * error, or give us the stat for FD 0). */
+ if (!(fd_is_set(fd, readfds) || fd_is_set(fd, writefds)))
+ return FALSE;
ret = fstat(fd, &stat_buf);
assert(!ret);
- return stat_buf.st_size > 0;
+ return (fd_is_set(fd, readfds) && S_READABLE(stat_buf.st_mode)) ||
+ (fd_is_set(fd, writefds) && S_WRITABLE(stat_buf.st_mode));
}
int select(int nfds, fd_set *readfds, fd_set *writefds,
@@ -162,11 +170,10 @@ int select(int nfds, fd_set *readfds, fd_set *writefds,
errno = EINVAL;
return -1;
}
- /* It is legal to select even if you didn't consume all of the data in
an
- * FD. Similar for writables, though it's harder for us to check those.
- * Hopefully we don't need to. */
+ /* It is legal to select on read even if you didn't consume all of the
data
+ * in an FD; similarly for writers on non-full FDs. */
for (int i = 0; i < nfds; i++) {
- if (fd_is_set(i, readfds) && fd_is_readable(i))
+ if (fd_is_actionable(i, readfds, writefds))
return nfds;
}
uth_mutex_lock(fdset_mtx);
--
2.8.0.rc3.226.g39d4020
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