Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
>> Jan Kiszka wrote:
>>> Gilles Chanteperdrix wrote:
>>>> Jan Kiszka wrote:
>>>>> Wait! When the sync object behind some file descriptor is deleted but
>>>>> the descriptor itself is still existing, we rather have to return that
>>>>> fd signaled from select() instead of letting the call fail. I beed to
>>>>> look into this again.
>>>> It looks to me like a transitory state, we can wait for the sync object
>>>> to be deleted to have the fd destructor signaled. It should not be long.
>>> That's not an issue of waiting for this. See e.g. TCP: peer closes
>>> connection -> internal sync objects will be destroyed (to make
>>> read/write fail). But the fd will remain valid until the local side
>>> closes it as well.
>> It looks to me like this is going to complicate things a lot, and will
>> be a source of regressions. Why can we not have sync objects be
>> destroyed when the fd is really destroyed and use a status bit of some
>> kind to signal read/write that the fd was closed by peer?
>
> It is way easier and more consistent to unblock reader and writers via
> destroying the sync object than to signal it and add tests for specific
> states to detect that. Keep in mind that this pattern is in use even
> without select support. Diverging from it just to add select awareness
> to some driver would be a step back.
>
First draft of a fix that so far does what it is supposed to do,
comments welcome:
diff --git a/ksrc/skins/posix/syscall.c b/ksrc/skins/posix/syscall.c
index 959b61c..4e46cb6 100644
--- a/ksrc/skins/posix/syscall.c
+++ b/ksrc/skins/posix/syscall.c
@@ -2298,24 +2298,30 @@ static int select_bind_one(struct xnselector *selector,
unsigned type, int fd)
}
static int select_bind_all(struct xnselector *selector,
- fd_set *fds[XNSELECT_MAX_TYPES], int nfds)
+ fd_set *in_fds[XNSELECT_MAX_TYPES],
+ fd_set *out_fds[XNSELECT_MAX_TYPES], int nfds)
{
unsigned fd, type;
+ int pending = 0;
int err;
for (type = 0; type < XNSELECT_MAX_TYPES; type++) {
- fd_set *set = fds[type];
+ fd_set *set = in_fds[type];
if (set)
for (fd = find_first_bit(set->fds_bits, nfds);
fd < nfds;
fd = find_next_bit(set->fds_bits, nfds, fd + 1)) {
err = select_bind_one(selector, type, fd);
- if (err)
- return err;
+ if (err) {
+ if (err != -EIDRM)
+ return err;
+ __FD_SET(fd, out_fds[type]);
+ pending++;
+ }
}
}
- return 0;
+ return pending;
}
/* int select(int, fd_set *, fd_set *, fd_set *, struct timeval *) */
@@ -2387,7 +2393,7 @@ static int __select(struct pt_regs *regs)
/* Bind directly the file descriptors, we do not need to go
through xnselect returning -ECHRNG */
- if ((err = select_bind_all(selector, in_fds, nfds)))
+ if ((err = select_bind_all(selector, in_fds, out_fds, nfds)))
return err;
}
@@ -2395,7 +2401,8 @@ static int __select(struct pt_regs *regs)
err = xnselect(selector, out_fds, in_fds, nfds, timeout, mode);
if (err == -ECHRNG) {
- int err = select_bind_all(selector, out_fds, nfds);
+ int err = select_bind_all(selector, out_fds, out_fds,
+ nfds);
if (err)
return err;
}
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