From 5a41aa6f4d5eb12a1fc2ef084d98f63d65f5fcc3 Mon Sep 17 00:00:00 2001 From: Michael Haubenwallner Date: Wed, 7 Dec 2016 11:58:29 +0100 Subject: [PATCH] forkables: Keep hardlinks disabled via shared mem. To avoid the need for each process to check the filesystem to detect that hardlink creation is impossible or disabled, cache this fact in shared memory. Removing cygfork directory while in use does disable hardlinks creation. To (re-)enable hardlinks creation, the cygfork directory has to exist before the first cygwin process does fork. * forkable.cc (dll_list::forkable_ntnamesize): Short cut forkables needs to impossible when disabled via shared memory. (dll_list::update_forkables_needs): When detecting hardlink creation as impossible (not on NTFS) while still (we are the first one checking) enabled via shared memory, disable the shared memory value. (dll_list::request_forkables): Disable the shared memory value when hardlinks creation became disabled, that is when the cygfork directory was removed. * include/cygwin/version.h: Bump CYGWIN_VERSION_SHARED_DATA 6. * shared_info.h (struct shared_info): Add member prefer_forkable_hardlinks. Update CURR_SHARED_MAGIC. * shared.cc (shared_info::initialize): Initialize prefer_forkable_hardlinks to 1 (Yes). --- winsup/cygwin/forkable.cc | 13 +++++++++++++ winsup/cygwin/include/cygwin/version.h | 2 +- winsup/cygwin/shared_info.h | 3 ++- 3 files changed, 16 insertions(+), 2 deletions(-) diff --git a/winsup/cygwin/forkable.cc b/winsup/cygwin/forkable.cc index cc28f9f4f..da45643ae 100644 --- a/winsup/cygwin/forkable.cc +++ b/winsup/cygwin/forkable.cc @@ -522,6 +522,11 @@ dll::create_forkable () size_t dll_list::forkable_ntnamesize (dll_type type, PCWCHAR fullntname, PCWCHAR modname) { + /* per process, this is the first forkables-method ever called */ + if (forkables_needs == forkables_unknown && + !cygwin_shared->prefer_forkable_hardlinks) + forkables_needs = forkables_impossible; /* short cut */ + if (forkables_needs == forkables_impossible) return 0; @@ -667,6 +672,7 @@ dll_list::update_forkables_needs () { debug_printf ("impossible, not on NTFS %W", fn.Buffer); forkables_needs = forkables_impossible; + cygwin_shared->prefer_forkable_hardlinks = 0; } } @@ -1056,6 +1062,13 @@ dll_list::request_forkables () set_forkables_inheritance (true); + if (forkables_needs == forkables_disabled) + { + /* we do not support (re-)enabling on the fly */ + forkables_needs = forkables_impossible; + cygwin_shared->prefer_forkable_hardlinks = 0; + } + if (forkables_needs <= forkables_needless) return; diff --git a/winsup/cygwin/include/cygwin/version.h b/winsup/cygwin/include/cygwin/version.h index 8926d49ae..f7ed351d3 100644 --- a/winsup/cygwin/include/cygwin/version.h +++ b/winsup/cygwin/include/cygwin/version.h @@ -518,7 +518,7 @@ details. */ regions. It is incremented when incompatible changes are made to the shared memory region *or* to any named shared mutexes, semaphores, etc. */ -#define CYGWIN_VERSION_SHARED_DATA 5 +#define CYGWIN_VERSION_SHARED_DATA 6 /* An identifier used in the names used to create shared objects. The full names include the CYGWIN_VERSION_SHARED_DATA version as well as this diff --git a/winsup/cygwin/shared_info.h b/winsup/cygwin/shared_info.h index 1a5648b24..8f0954f50 100644 --- a/winsup/cygwin/shared_info.h +++ b/winsup/cygwin/shared_info.h @@ -33,7 +33,7 @@ public: /* Data accessible to all tasks */ -#define CURR_SHARED_MAGIC 0x6758de88U +#define CURR_SHARED_MAGIC 0x3a6025edU #define USER_VERSION 1 @@ -51,6 +51,7 @@ class shared_info mtinfo mt; loadavginfo loadavg; LONG pid_src; + char prefer_forkable_hardlinks; /* single byte access always is atomic */ void initialize (); void init_obcaseinsensitive ();