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[libvirt] [libvirt-python][PATCH v2 4/4] examples: Introduce sparsestream.py



Sparse streams are not that straight forward to use for the very
first time. Especially the sparseRecvAll() and sparseSendAll()
methods which expects callbacks. What we can do to make it easier
for developers is to have an example where they can take an
inspiration from.

Signed-off-by: Michal Privoznik <mprivozn redhat com>
---
 examples/sparsestream.py | 117 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 117 insertions(+)
 create mode 100755 examples/sparsestream.py

diff --git a/examples/sparsestream.py b/examples/sparsestream.py
new file mode 100755
index 0000000..e960c40
--- /dev/null
+++ b/examples/sparsestream.py
@@ -0,0 +1,117 @@
+#!/usr/bin/env python
+# Example of sparse streams usage
+#
+# Authors:
+#   Michal Privoznik <mprivozn redhat com>
+
+import libvirt, sys, os
+
+def bytesWriteHandler(stream, buf, opaque):
+    fd = opaque
+    return os.write(fd, buf)
+
+def bytesReadHandler(stream, nbytes, opaque):
+    fd = opaque
+    return os.read(fd, nbytes)
+
+def recvSkipHandler(stream, length, opaque):
+    fd = opaque
+    cur = os.lseek(fd, length, os.SEEK_CUR)
+    return os.ftruncate(fd, cur)
+
+def sendSkipHandler(stream, length, opaque):
+    fd = opaque
+    return os.lseek(fd, length, os.SEEK_CUR)
+
+def holeHandler(stream, opaque):
+    fd = opaque
+    cur = os.lseek(fd, 0, os.SEEK_CUR)
+
+    try:
+        data = os.lseek(fd, cur, os.SEEK_DATA)
+    except OSError as e:
+        if e.errno != 6:
+            raise e
+        else:
+            data = -1;
+    # There are three options:
+    # 1) data == cur;  @cur is in data
+    # 2) data > cur; @cur is in a hole, next data at @data
+    # 3) data < 0; either @cur is in trailing hole, or @cur is beyond EOF.
+    if data < 0:
+        # case 3
+        inData = False
+        eof = os.lseek(fd, 0, os.SEEK_END)
+        if (eof < cur):
+            raise RuntimeError("Current position in file after EOF: %d" % cur)
+        sectionLen = eof - cur
+    else:
+        if (data > cur):
+            # case 2
+            inData = False
+            sectionLen = data - cur
+        else:
+            # case 1
+            inData = True
+
+            # We don't know where does the next hole start. Let's find out.
+            # Here we get the same options as above
+            hole = os.lseek(fd, data, os.SEEK_HOLE)
+            if hole < 0:
+                # case 3. But wait a second. There is always a trailing hole.
+                # Do the best what we can here
+                raise RuntimeError("No trailing hole")
+
+            if (hole == data):
+                # case 1. Again, this is suspicious. The reason we are here is
+                # because we are in data. But at the same time we are in a
+                # hole. WAT?
+                raise RuntimeError("Impossible happened")
+            else:
+                # case 2
+                sectionLen = hole - data
+    os.lseek(fd, cur, os.SEEK_SET)
+    return [inData, sectionLen]
+
+def download(vol, st, filename):
+    offset = 0
+    length = 0
+
+    fd = os.open(filename, os.O_WRONLY | os.O_CREAT | os.O_TRUNC, mode=0o0660)
+    vol.download(st, offset, length, libvirt.VIR_STORAGE_VOL_DOWNLOAD_SPARSE_STREAM)
+    st.sparseRecvAll(bytesWriteHandler, recvSkipHandler, fd)
+
+    os.close(fd)
+
+def upload(vol, st, filename):
+    offset = 0
+    length = 0
+
+    fd = os.open(filename, os.O_RDONLY)
+    vol.upload(st, offset, length, libvirt.VIR_STORAGE_VOL_UPLOAD_SPARSE_STREAM)
+    st.sparseSendAll(bytesReadHandler, holeHandler, sendSkipHandler, fd)
+
+    os.close(fd)
+
+# main
+if len(sys.argv) != 5:
+    print("Usage: ", sys.argv[0], " URI --upload/--download VOLUME FILE")
+    print("Either uploads local FILE to libvirt VOLUME, or downloads libvirt ")
+    print("VOLUME into local FILE while preserving FILE/VOLUME sparseness")
+    sys.exit(1)
+
+conn = libvirt.open(sys.argv[1])
+vol = conn.storageVolLookupByKey(sys.argv[3])
+
+st = conn.newStream()
+
+if sys.argv[2] == "--download":
+    download(vol, st, sys.argv[4])
+elif sys.argv[2] == "--upload":
+    upload(vol, st, sys.argv[4])
+else:
+    print("Unknown operation: %s " % sys.argv[1])
+    sys.exit(1)
+
+st.finish()
+conn.close()
-- 
2.13.0


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