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Cygwin: //server: check existence of server with getaddrinfo

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Checking server existence by trying to enumerate its shares
may result in 2 minutes delay until some internal timeout is hit.

In the light that every network is an IP network anyway these
days, let's try with a simple getaddrinfo() call.  This is usually
back in 3 secs even if the server doesn't exist, and it's usually
back in 8 secs if the DNS server can't be connected.  This is the
fastest method I found to check server existence yet.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2024-03-22 15:34:29 +01:00
parent 290843bbda
commit 8d2c1b4ce6
1 changed files with 24 additions and 27 deletions
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51
winsup/cygwin/fhandler/netdrive.cc
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@ -15,9 +15,11 @@ details. */
#include "cygheap.h"
#include "cygthread.h"
#define USE_SYS_TYPES_FD_SET
#include <shobjidl.h>
#include <shlobj.h>
#include <lm.h>
#include <ws2tcpip.h>
#include <stdlib.h>
#include <dirent.h>
@ -94,23 +96,14 @@ struct netdriveinf
{
DIR *dir;
int err;
bool test_only;
HANDLE sem;
};
static inline int
hresult_to_errno (HRESULT wres, bool test_only = false)
hresult_to_errno (HRESULT wres)
{
if (SUCCEEDED (wres))
return 0;
/* IEnumShellItems::Reset returns E_NOTIMPL when called for share
enumeration. However, if the machine doesn't exist, the Win32
error ERROR_BAD_NETPATH (converted into a HRESULT) is returned. In
test_only mode, we exploit this. Also, E_ACCESSDENIED is a funny
one. It means, the machine exists, you just have no right to
access the share list, or SMB doesn't run. */
if (test_only && (wres == E_NOTIMPL || wres == E_ACCESSDENIED))
return 0;
if (((ULONG) wres & 0xffff0000)
== (ULONG) MAKE_HRESULT(SEVERITY_ERROR, FACILITY_WIN32, 0))
return geterrno_from_win_error ((ULONG) wres & 0xffff);
@ -174,18 +167,9 @@ thread_netdrive (void *arg)
goto out;
}
if (len == 2 || ndi->test_only)
if (len == 2)
{
wres = netitem_enum->Reset ();
if (FAILED (wres) || ndi->test_only)
{
ndi->err = hresult_to_errno (wres, ndi->test_only);
netitem_enum->Release ();
netparent->Release ();
goto out;
}
netitem_enum->Reset ();
/* Don't look at me!
Network discovery is very unreliable and the list of machines
@ -244,9 +228,9 @@ out:
}
static DWORD
create_thread_and_wait (DIR *dir, bool test_only)
create_thread_and_wait (DIR *dir)
{
netdriveinf ndi = { dir, 0, test_only,
netdriveinf ndi = { dir, 0,
CreateSemaphore (&sec_none_nih, 0, 2, NULL) };
cygthread *thr = new cygthread (thread_netdrive, &ndi, "netdrive");
@ -262,9 +246,22 @@ fhandler_netdrive::exists ()
if (strlen (get_name ()) == 2)
return virt_rootdir;
DIR dir = { 0 };
dir.__d_dirname = (char *) get_name ();
int ret = create_thread_and_wait (&dir, true);
wchar_t name[MAX_PATH];
struct addrinfoW *ai;
INT ret;
/* Hopefully we are allowed to assume an IP network with existing name
resolution these days. Therefore, just try to resolve the name
into IP addresses. This may take up to about 3 secs if the name
doesn't exist, or about 8 secs if DNS is unavailable.
Don't ask for "tsclient", it doesn't resolve. Just assume it exists. */
if (!strcmp (get_name () + 2, "tsclient"))
return virt_directory;
sys_mbstowcs (name, CYG_MAX_PATH, get_name ());
ret = GetAddrInfoW (name + 2, NULL, NULL, &ai);
if (!ret)
FreeAddrInfoW (ai);
return ret ? virt_none : virt_directory;
}
@ -295,7 +292,7 @@ fhandler_netdrive::opendir (int fd)
int ret;
dir = fhandler_virtual::opendir (fd);
if (dir && (ret = create_thread_and_wait (dir, false)))
if (dir && (ret = create_thread_and_wait (dir)))
{
free (dir->__d_dirname);
free (dir->__d_dirent);