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The following commit(s) were added to refs/heads/master by this push:
new 02a168d7866 fs/vfs: Report POLLERR in the read and write sets of
select().
02a168d7866 is described below
commit 02a168d786608f39db8278ec5e825f1011f456f3
Author: Marco Casaroli <[email protected]>
AuthorDate: Tue Oct 13 22:59:48 2026 +0200
fs/vfs: Report POLLERR in the read and write sets of select().
select() put a descriptor with POLLERR only in exceptfds. A caller that
asked only for readfds or writefds did not see the error: select()
returned 0, also with no timeout, where 0 means that the timeout
expired. POSIX says that a descriptor is ready for reading or writing
when the call would not block, also when it would return an error.
For example, a fifth thread that polls a pipe with
CONFIG_DEV_PIPE_NPOLLWAITERS=4 gets POLLERR, and its select() with no
timeout returned 0 at once.
Report POLLERR in readfds and writefds, as Linux does. poll() reports
POLLHUP and POLLERR also when they were not asked for, so set only the
bits of the sets that the caller asked for.
Assisted-by: Claude Code:claude-opus-5-5
Signed-off-by: Marco Casaroli <[email protected]>
---
fs/vfs/fs_select.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/fs/vfs/fs_select.c b/fs/vfs/fs_select.c
index d9bf848b26c..6815fee4321 100644
--- a/fs/vfs/fs_select.c
+++ b/fs/vfs/fs_select.c
@@ -245,11 +245,16 @@ int select(int nfds, FAR fd_set *readfds, FAR fd_set
*writefds,
* read condition. POLLHUP will be reported when no more data will
* be available (such as when a connection is lost). In either
* case, the read() can then be performed without blocking.
+ *
+ * POLLERR is a read and a write condition too: a read() or a
+ * write() then returns at once, with an error. poll() reports
+ * POLLHUP and POLLERR even when they were not asked for, so set
+ * only the bits that the caller asked for.
*/
- if (readfds)
+ if (readfds && (pollset[ndx].events & POLLIN) != 0)
{
- if (pollset[ndx].revents & (POLLIN | POLLHUP))
+ if (pollset[ndx].revents & (POLLIN | POLLHUP | POLLERR))
{
FD_SET(pollset[ndx].fd, readfds);
ret++;
@@ -258,9 +263,9 @@ int select(int nfds, FAR fd_set *readfds, FAR fd_set
*writefds,
/* Check for write conditions */
- if (writefds)
+ if (writefds && (pollset[ndx].events & POLLOUT) != 0)
{
- if (pollset[ndx].revents & (POLLOUT | POLLHUP))
+ if (pollset[ndx].revents & (POLLOUT | POLLHUP | POLLERR))
{
FD_SET(pollset[ndx].fd, writefds);
ret++;
