.

wcfs/client/client_test.py

@@ -173,6 +173,7 @@ def test_wcfs_client():
 
     # XXX wconn.open()      after wconn.close() -> error
     # XXX wconn.resync()    after wconn.close() -> error
+
     # XXX all fileh / mappings become invalid after wconn.close
 
 

wcfs/client/wcfs.cpp

@@ -198,6 +198,7 @@ using std::vector;
 namespace wcfs {
 
 static error mmap_zero_into_ro(void *addr, size_t size);
+static error mmap_efault_into(void *addr, size_t size);
 static tuple<uint8_t*, error> mmap_ro(os::File f, off_t offset, size_t size);
 static error mmap_into_ro(void *addr, size_t size, os::File f, off_t offset);
 
@@ -412,7 +413,7 @@ error _Conn::__pin1(PinReq *req) {
     // So if we take virt_lock right around mmap._remmapblk(), the order of
     // locks in pinner would be
     //
-    //      wconn.atMu.R, wconn.filehMu.R, f.mu, virt_lock
+    //      wconn.atMu.R, wconn.filehMu.R, fileh.mu, virt_lock
     //
     // which means there is AB-BA deadlock possibility.
     //
@@ -810,6 +811,8 @@ error _FileH::close() {
     _FileH& fileh = *this;
     Conn    wconn = fileh.wconn;
 
+    // XXX virt_lock + explain (refer to __pin1)
+
     wconn->_atMu.RLock();
     wconn->_filehMu.Lock();
     defer([&]() {
@@ -1023,6 +1026,8 @@ error _Mapping::unmap() {
 // - f.wconn.atMu
 // - f._mu          XXX not needed? (f._mmaps and f._pinned are not used)
 error _Mapping::_remmapblk(int64_t blk, zodb::Tid at) {
+    // XXX must not be called after Mapping is switched to efault?
+
     _Mapping *mmap = this;
     FileH f = mmap->fileh;
     xerr::Contextf E("%s: f<%s>: remmapblk #%ld @%s", v(f->wconn), v(f->foid), blk, v(at));
@@ -1093,6 +1098,8 @@ error _Mapping::remmap_blk(int64_t blk) {
     if (!(mmap.blk_start <= blk && blk < mmap.blk_stop()))
         panic("remmap_blk: blk out of Mapping range");
 
+    // XXX do nothing after mapping is switched to efault? (i.e. f is closed/down)
+
     // blkrev = rev | @head
     zodb::Tid blkrev; bool ok;
     tie(blkrev, ok) = f->_pinned.get_(blk);
@@ -1125,9 +1132,8 @@ tuple<os::File, error> WCFS::_open(const string &path, int flags) {
 
 // ---- misc ----
 
-// mmap_zero_into_ro mmaps read-only zeros into [addr +size) so that region is all zeros.
-// created mapping, even after it is accessed, does not consume memory.
-static error mmap_zero_into_ro(void *addr, size_t size) {
+// mmap_zero_into serves mmap_zero_into_ro and mmap_efault_into.
+static error mmap_zero_into(void *addr, size_t size, int prot) {
     xerr::Contextf E("mmap zero");
     etrace("");
 
@@ -1141,12 +1147,29 @@ static error mmap_zero_into_ro(void *addr, size_t size) {
     defer([&]() {
         z->close();
     });
-    err = mm::map_into(addr, size, PROT_READ, MAP_SHARED | MAP_NORESERVE, z, 0);
+    err = mm::map_into(addr, size, prot, MAP_SHARED | MAP_NORESERVE, z, 0);
     if (err != nil)
         return E(err);
     return nil;
 }
 
+// mmap_zero_into_ro mmaps read-only zeros into [addr +size) so that region is all zeros.
+// created mapping, even after it is accessed, does not consume memory.
+static error mmap_zero_into_ro(void *addr, size_t size) {
+    return mmap_zero_into(addr, size, PROT_READ);
+}
+
+// mmap_efault_into changes [addr +size) region to generate SIGSEGV on read/write access.
+// Any previous mapping residing in that virtual address range is released.
+static error mmap_efault_into(void *addr, size_t size) {
+    xerr::Contextf E("mmap efault");
+    etrace("");
+
+    // mmaping /dev/zero with PROT_NONE gives what we need.
+    return E(mmap_zero_into(addr, size, PROT_NONE));
+}
+
+
 // mmap_ro mmaps read-only fd[offset +size).
 // The mapping is created with MAP_SHARED.
 static tuple<uint8_t*, error> mmap_ro(os::File f, off_t offset, size_t size) {