Use posix_spawn to run the pager

In low memory environments, "nix-env -qa" failed because the fork to
run the pager hit the kernel's overcommit limits. Using posix_spawn
gets around this. (Actually, you have to use posix_spawn with the
undocumented POSIX_SPAWN_USEVFORK flag, otherwise it just uses
fork/exec...)

2 files changed, 9 insertions, 2 deletions

diff --git a/src/libutil/types.hh b/src/libutil/types.hh
index 160884ee1a..030996a060 100644
--- a/src/libutil/types.hh
+++ b/src/libutil/types.hh
@@ -73,6 +73,7 @@ class SysError : public Error
 public:
     int errNo;
     SysError(const FormatOrString & fs);
+    SysError(int errNo, const FormatOrString & fs);
 };
 
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 305e470ebd..60be02cd46 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -45,8 +45,14 @@ BaseError & BaseError::addPrefix(const FormatOrString & fs)
 
 
 SysError::SysError(const FormatOrString & fs)
-    : Error(format("%1%: %2%") % fs.s % strerror(errno))
-    , errNo(errno)
+    : SysError(errno, fs)
+{
+}
+
+
+SysError::SysError(int errNo, const FormatOrString & fs)
+    : Error(format("%1%: %2%") % fs.s % strerror(errNo))
+    , errNo(errNo)
 {
 }