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hurd: Avoid extra ctty RPCs in init_dtable ()

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It is common to have (some of) stdin, stdout and stderr point to the
very same port. We were making the ctty RPCs that _hurd_port2fd () does
for each one of them separately:

1. term_getctty ()
2. mach_port_deallocate ()
3. term_open_ctty ()

Instead, let's detect this case and duplicate the ctty port we already
have. This means we do 1 RPC instead of 3 (and create a single protid
on the server side) if the file is our ctty, and no RPCs instead of 1
if it's not. A clear win!

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
This commit is contained in:
Sergey Bugaev 2023-04-15 19:17:18 +03:00 committed by Samuel Thibault
parent 76d0f094dd
commit e55a55acb1
1 changed files with 38 additions and 6 deletions
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44
hurd/dtable.c
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@ -60,18 +60,50 @@ init_dtable (void)
_hurd_dtable[i] = NULL;
else
{
int copy;
/* Allocate a new file descriptor structure. */
struct hurd_fd *new = malloc (sizeof (struct hurd_fd));
if (new == NULL)
__libc_fatal ("hurd: Can't allocate initial file descriptors\n");
/* Initialize the port cells. */
_hurd_port_init (&new->port, MACH_PORT_NULL);
_hurd_port_init (&new->ctty, MACH_PORT_NULL);
/* See if this file descriptor is the same as a previous one we have
already installed. In this case, we can just copy over the same
ctty port without making any more RPCs. We only check the the
immediately preceding fd and fd 0 -- this should be enough to
handle the common cases while not requiring quadratic
complexity. */
if (i > 0 && _hurd_init_dtable[i] == _hurd_init_dtable[i - 1])
copy = i - 1;
else if (i > 0 && _hurd_init_dtable[i] == _hurd_init_dtable[0])
copy = 0;
else
copy = -1;
/* Install the port in the descriptor.
This sets up all the ctty magic. */
_hurd_port2fd (new, _hurd_init_dtable[i], 0);
if (copy < 0)
{
/* Initialize the port cells. */
_hurd_port_init (&new->port, MACH_PORT_NULL);
_hurd_port_init (&new->ctty, MACH_PORT_NULL);
/* Install the port in the descriptor.
This sets up all the ctty magic. */
_hurd_port2fd (new, _hurd_init_dtable[i], 0);
}
else
{
/* Copy over ctty from the already set up file descriptor that
contains the same port. We can access the contents of the
cell without any locking since no one could have seen it
yet. */
mach_port_t ctty = _hurd_dtable[copy]->ctty.port;
if (MACH_PORT_VALID (ctty))
__mach_port_mod_refs (__mach_task_self (), ctty,
MACH_PORT_RIGHT_SEND, +1);
_hurd_port_init (&new->port, _hurd_init_dtable[i]);
_hurd_port_init (&new->ctty, ctty);
}
_hurd_dtable[i] = new;
}