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files: Formalize fd restore priorities

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There are places when we have to select which fd to ->open
and which to ->receive. To avoid deadlocks we sort them in
an ascending order on { pid, fd } pair.

Make this idea more formal by introducing an explicit function
doing this check and call it where appropriate (pipe.c master
selection is also simplified to fit new ... API).

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
This commit is contained in:
Pavel Emelyanov
2012-09-14 22:09:22 +04:00
parent a0560c4298
commit 8fc6dbfadd
4 changed files with 13 additions and 14 deletions
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6
include/files.h
View File

@@ -43,6 +43,12 @@ struct fdinfo_list_entry {
FdinfoEntry *fe;
};
/* reports whether fd_a takes prio over fd_b */
static inline int fdinfo_rst_prio(struct fdinfo_list_entry *fd_a, struct fdinfo_list_entry *fd_b)
{
return (fd_a->pid < fd_b->pid) || ((fd_a->pid == fd_b->pid) && (fd_a->fe->fd < fd_b->fe->fd));
}
struct file_desc_ops {
unsigned int type;
int (*open)(struct file_desc *d);

14
pipes.c
View File

@@ -112,7 +112,6 @@ void mark_pipe_master(void)
while (1) {
struct fdinfo_list_entry *fle;
struct pipe_info *pi, *pic, *p;
int fd, pid;
if (list_empty(&pipes))
break;
@@ -125,18 +124,15 @@ void mark_pipe_master(void)
fle = file_master(&pi->d);
p = pi;
fd = fle->fe->fd;
pid = fle->pid;
list_for_each_entry(pic, &pi->pipe_list, pipe_list) {
list_move(&pic->list, &head);
struct fdinfo_list_entry *f;
fle = file_master(&pic->d);
if (fle->pid < pid ||
(pid == fle->pid && fle->fe->fd < fd)) {
list_move(&pic->list, &head);
f = file_master(&pic->d);
if (fdinfo_rst_prio(f, fle)) {
p = pic;
fd = fle->fe->fd;
pid = fle->pid;
fle = f;
}
show_saved_pipe_fds(pic);

4
sk-unix.c
View File

@@ -762,9 +762,7 @@ int resolve_unix_peers(void)
fle = file_master(&ui->d);
fle_peer = file_master(&peer->d);
if ((fle->pid < fle_peer->pid) ||
(fle->pid == fle_peer->pid &&
fle->fe->fd < fle_peer->fe->fd)) {
if (fdinfo_rst_prio(fle, fle_peer)) {
ui->flags |= USK_PAIR_MASTER;
peer->flags |= USK_PAIR_SLAVE;
} else {

3
tty.c
View File

@@ -670,8 +670,7 @@ static void tty_setup_orphan_slavery(void)
* waiting for each other.
*/
b = file_master(&peer->d);
if (a->pid > b->pid ||
(a->pid == b->pid && a->fe->fd > b->fe->fd)) {
if (fdinfo_rst_prio(b, a)) {
a = b;
m = peer;
}