[RFC PATCH] Allow more file descriptors than clients limit

[Olivier Fourdan]

Hi

I've filed bug https://bugs.freedesktop.org/show_bug.cgi?id=91072 to keep track of this issue and copying Wayland-devel ML as well since this is affecting Wayland/XWayland primarily.

Cheers,
Olivier

----- Original Message -----
> The X server assumes that one file descriptor is opened per client, so
> it limits the number of file descriptors to the number of clients.
> 
> Unfortunately Xwayland opens a lot more file descriptors than a regular
> X server because of those "weston-shared-XXXXXX" anonymous files for
> sharing buffers. The number of additional file descriptors opened depends
> on the clients so the actual limit depends on what applications are
> running.
> 
> Once the X server (Xwayland) reaches the maximum number of file
> descriptors opened, it will raise a "Maximum number of clients reached"
> error and deny new connections even if the actual number of clients is
> a lot less that the expected limit, thus limiting  the number of clients
> in Xwayland to a much lower value than the expected default limit of 256
> clients.
> 
> Raise the limit of file descriptors to match XFD_SETSIZE set in Xproto
> while retaining the current limit of clients to a lower value, allowing
> for more usable clients in Xwayland (even if the client limit will
> remain a theoretical limit unlikely to be reachable in Xwayland).
> 
> Signed-off-by: Olivier Fourdan <ofourdan at redhat.com>
> ---
> See also: http://lists.x.org/archives/xorg-devel/2015-May/046543.html
> 
>  include/opaque.h |  1 +
>  os/WaitFor.c     |  4 ++--
>  os/connection.c  | 38 ++++++++++++++++++--------------------
>  3 files changed, 21 insertions(+), 22 deletions(-)
> 
> diff --git a/include/opaque.h b/include/opaque.h
> index a2c54aa..99e310e 100644
> --- a/include/opaque.h
> +++ b/include/opaque.h
> @@ -36,6 +36,7 @@ from The Open Group.
>  extern _X_EXPORT const char *defaultTextFont;
>  extern _X_EXPORT const char *defaultCursorFont;
>  extern _X_EXPORT int MaxClients;
> +extern _X_EXPORT int limitFileDesc;
>  extern _X_EXPORT volatile char isItTimeToYield;
>  extern _X_EXPORT volatile char dispatchException;
>  
> diff --git a/os/WaitFor.c b/os/WaitFor.c
> index 431f1a6..74e0b2e 100644
> --- a/os/WaitFor.c
> +++ b/os/WaitFor.c
> @@ -220,10 +220,10 @@ WaitForSomething(int *pClientsReady)
>              i = -1;
>          else if (AnyClientsWriteBlocked) {
>              XFD_COPYSET(&ClientsWriteBlocked, &clientsWritable);
> -            i = Select(MaxClients, &LastSelectMask, &clientsWritable, NULL,
> wt);
> +            i = Select(limitFileDesc, &LastSelectMask, &clientsWritable,
> NULL, wt);
>          }
>          else {
> -            i = Select(MaxClients, &LastSelectMask, NULL, NULL, wt);
> +            i = Select(limitFileDesc, &LastSelectMask, NULL, NULL, wt);
>          }
>          selecterr = GetErrno();
>          WakeupHandler(i, (void *) &LastSelectMask);
> diff --git a/os/connection.c b/os/connection.c
> index c36b125..4df6a67 100644
> --- a/os/connection.c
> +++ b/os/connection.c
> @@ -119,7 +119,7 @@ SOFTWARE.
>  
>  #include "probes.h"
>  
> -static int lastfdesc;           /* maximum file descriptor */
> +int limitFileDesc = -1;           /* maximum file descriptor */
>  
>  fd_set WellKnownConnections;    /* Listener mask */
>  fd_set EnabledDevices;          /* mask for input devices that are on */
> @@ -264,44 +264,42 @@ lookup_trans_conn(int fd)
>      return NULL;
>  }
>  
> -/* Set MaxClients and lastfdesc, and allocate ConnectionTranslation */
> +/* Set MaxClients and limitFileDesc, and allocate ConnectionTranslation */
>  
>  void
>  InitConnectionLimits(void)
>  {
> -    lastfdesc = -1;
> -
>  #ifndef __CYGWIN__
>  
>  #if !defined(XNO_SYSCONF) && defined(_SC_OPEN_MAX)
> -    lastfdesc = sysconf(_SC_OPEN_MAX) - 1;
> +    limitFileDesc = sysconf(_SC_OPEN_MAX) - 1;
>  #endif
>  
>  #ifdef HAVE_GETDTABLESIZE
> -    if (lastfdesc < 0)
> -        lastfdesc = getdtablesize() - 1;
> +    if (limitFileDesc < 0)
> +        limitFileDesc = getdtablesize() - 1;
>  #endif
>  
>  #ifdef _NFILE
> -    if (lastfdesc < 0)
> -        lastfdesc = _NFILE - 1;
> +    if (limitFileDesc < 0)
> +        limitFileDesc = _NFILE - 1;
>  #endif
>  
>  #endif                          /* __CYGWIN__ */
>  
>      /* This is the fallback */
> -    if (lastfdesc < 0)
> -        lastfdesc = MAXSOCKS;
> +    if (limitFileDesc < 0)
> +        limitFileDesc = MAXSOCKS;
>  
> -    if (lastfdesc > MAXSELECT)
> -        lastfdesc = MAXSELECT;
> +    if (limitFileDesc > MAXSELECT)
> +        limitFileDesc = MAXSELECT;
>  
> -    if (lastfdesc > MAXCLIENTS) {
> -        lastfdesc = MAXCLIENTS;
> +    if (limitFileDesc > XFD_SETSIZE) {
> +        limitFileDesc = XFD_SETSIZE;
>          if (debug_conns)
> -            ErrorF("REACHED MAXIMUM CLIENTS LIMIT %d\n", MAXCLIENTS);
> +            ErrorF("REACHED MAXIMUM CONNECTIONS LIMIT %d\n", XFD_SETSIZE);
>      }
> -    MaxClients = lastfdesc;
> +    MaxClients = MIN(MAXCLIENTS, limitFileDesc);
>  
>  #ifdef DEBUG
>      ErrorF("InitConnectionLimits: MaxClients = %d\n", MaxClients);
> @@ -309,7 +307,7 @@ InitConnectionLimits(void)
>  
>  #if !defined(WIN32)
>      if (!ConnectionTranslation)
> -        ConnectionTranslation = xnfallocarray(lastfdesc + 1, sizeof(int));
> +        ConnectionTranslation = xnfallocarray(limitFileDesc + 1,
> sizeof(int));
>  #else
>      InitConnectionTranslation();
>  #endif
> @@ -754,7 +752,7 @@ AllocNewConnection(XtransConnInfo trans_conn, int fd,
> CARD32 conn_time)
>  
>      if (
>  #ifndef WIN32
> -           fd >= lastfdesc
> +           fd >= limitFileDesc
>  #else
>             XFD_SETCOUNT(&AllClients) >= MaxClients
>  #endif
> @@ -859,7 +857,7 @@ EstablishNewConnections(ClientPtr clientUnused, void
> *closure)
>  
>          newconn = _XSERVTransGetConnectionNumber(new_trans_conn);
>  
> -        if (newconn < lastfdesc) {
> +        if (newconn < limitFileDesc) {
>              int clientid;
>  
>  #if !defined(WIN32)
> --
> 2.4.3
> 
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