[gem5-dev] changeset in gem5: dev: Add post-fork handling for disk images

[Andreas Sandberg]

changeset 17e33647b5d1 in /z/repo/gem5
details: http://repo.gem5.org/gem5?cmd=changeset;node=17e33647b5d1
description:
        dev: Add post-fork handling for disk images

        This changeset adds support for notifying the disk images that the 
simulator has
        been forked. We need to disable the saving of the CoW disk image from 
the child
        process, and we need to make sure that systems which use a raw disk 
image are
        not allowed to fork to avoid two or more gem5 processes writing to the 
same disk
        image.

        Signed-off-by: Andreas Sandberg <andr...@sandberg.pp.se>
        [sascha.bisch...@arm.com: Rebased patches onto a newer gem5 version]
        Signed-off-by: Sascha Bischoff <sascha.bisch...@arm.com>
        Signed-off-by: Andreas Sandberg <andreas.sandb...@arm.com>

diffstat:

 src/dev/storage/disk_image.cc |  29 +++++++++++++++++++++++++++--
 src/dev/storage/disk_image.hh |   4 ++++
 2 files changed, 31 insertions(+), 2 deletions(-)

diffs (74 lines):

diff -r 40be59176869 -r 17e33647b5d1 src/dev/storage/disk_image.cc
--- a/src/dev/storage/disk_image.cc     Thu Nov 26 10:03:43 2015 +0000
+++ b/src/dev/storage/disk_image.cc     Thu Nov 26 10:11:52 2015 +0000
@@ -65,6 +65,17 @@
 { close(); }
 
 void
+RawDiskImage::notifyFork()
+{
+    if (initialized && !readonly)
+        panic("Attempting to fork system with read-write raw disk image.");
+
+    const Params *p(dynamic_cast<const Params *>(params()));
+    close();
+    open(p->image_file, p->read_only);
+}
+
+void
 RawDiskImage::open(const string &filename, bool rd_only)
 {
     if (!filename.empty()) {
@@ -198,6 +209,16 @@
 }
 
 void
+CowDiskImage::notifyFork()
+{
+    if (!dynamic_cast<const Params *>(params())->read_only &&
+        !filename.empty()) {
+        inform("Disabling saving of COW image in forked child process.\n");
+        filename = "";
+    }
+}
+
+void
 SafeRead(ifstream &stream, void *data, int count)
 {
     stream.read((char *)data, count);
@@ -311,8 +332,12 @@
 void
 CowDiskImage::save() const
 {
-    save(filename);
-}
+    // filename will be set to the empty string to disable saving of
+    // the COW image in a forked child process. Save will still be
+    // called because there is no easy way to unregister the exit
+    // callback.
+    if (!filename.empty())
+        save(filename);}
 
 void
 CowDiskImage::save(const string &file) const
diff -r 40be59176869 -r 17e33647b5d1 src/dev/storage/disk_image.hh
--- a/src/dev/storage/disk_image.hh     Thu Nov 26 10:03:43 2015 +0000
+++ b/src/dev/storage/disk_image.hh     Thu Nov 26 10:11:52 2015 +0000
@@ -82,6 +82,8 @@
     RawDiskImage(const Params *p);
     ~RawDiskImage();
 
+    void notifyFork() override;
+
     void close();
     void open(const std::string &filename, bool rd_only = false);
 
@@ -123,6 +125,8 @@
     CowDiskImage(const Params *p);
     ~CowDiskImage();
 
+    void notifyFork() override;
+
     void initSectorTable(int hash_size);
     bool open(const std::string &file);
     void save() const;
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