check for sync_file_range and patch

README.md

@@ -11,11 +11,14 @@ How to use:
  - run "apt update; apt install git"
  - run "git clone https://github.com/ravenschade/borgbackup_on_android.git"
  - run "cd borgbackup_on_android; bash build.sh"
-- (if virtualenv for python does not work properly you have to set selinux to permissive (do "/system/bin/setenforce 0" with root permissions))
+ - (if virtualenv for python does not work properly you have to set selinux to permissive (do "/system/bin/setenforce 0" with root permissions))
+
+Known issues:
+ - borg starting at 1.1 requires the system call sync_file_range (see https://github.com/borgbackup/borg/pull/985 and https://github.com/borgbackup/borg/issues/1961). The linux subsystem in Windows 10 and some older Android versions (for example Lineage including 14.1) do not yet have this. Lineage 15.0 has this call and should work. I have added a test to the build script that checks if sync_file_range is available. If it is not, then I apply a patch (borg_sync_file_range.patch) that replaces this sync with convential file syncs.
 
 Tested with:
 - termux 0.56
-- borg 1.1.3
+- borg 1.0.12, 1.1.3
 
 Tested and working so far is:
 - creation of repositories 

borg_sync_file_range.patch

@@ -0,0 +1,16 @@
+diff --git a/src/borg/platform/linux.pyx b/src/borg/platform/linux.pyx
+index 25f71fa1..42ffa85f 100644
+--- a/src/borg/platform/linux.pyx
++++ b/src/borg/platform/linux.pyx
+@@ -225,8 +225,9 @@ def acl_set(path, item, numeric_owner=False):
+ cdef _sync_file_range(fd, offset, length, flags):
+     assert offset & PAGE_MASK == 0, "offset %d not page-aligned" % offset
+     assert length & PAGE_MASK == 0, "length %d not page-aligned" % length
+-    if sync_file_range(fd, offset, length, flags) != 0:
+-        raise OSError(errno.errno, os.strerror(errno.errno))
++    os.fdatasync(fd)
++    #if sync_file_range(fd, offset, length, flags) != 0:
++    #    raise OSError(errno.errno, os.strerror(errno.errno))
+     safe_fadvise(fd, offset, length, 'DONTNEED')
+ 
+ cdef unsigned PAGE_MASK = sysconf(_SC_PAGESIZE) - 1

build.sh

@@ -14,6 +14,16 @@ git checkout 1.1-maint
 
 pip install -r requirements.d/development.txt
 
+#find if sync_file_range is available
+s=`bash ../sync_file_range_test/test.sh`
+if [ "$s" = "1" ];
+then
+	echo "patching borg to not use sync_file_range...."
+	git apply ../borg_sync_file_range.patch
+else
+	echo "no need to patch borg"
+fi
+
 #download and build lz4
 wget https://github.com/lz4/lz4/archive/v1.7.5.tar.gz -O lz4.tar.gz
 tar -xf lz4.tar.gz

sync_file_range_test/setup.py

@@ -0,0 +1,6 @@
+# setup.py - unnecessary if not redistributing the code, see below
+from setuptools import setup
+from Cython.Build import cythonize
+
+setup(name = 'Hello world app',
+      ext_modules = cythonize("*.pyx"))

sync_file_range_test/sync_file_range_test.py

@@ -0,0 +1,6 @@
+try:
+    import sync_file_range_test
+except ImportError:
+    raise ImportError('sync_file_range not existent')
+
+sync_file_range_test.sync_file_range_test(0)

sync_file_range_test/sync_file_range_test.pyx

@@ -0,0 +1,11 @@
+
+cdef extern from "fcntl.h":
+     int sync_file_range(int fd, int offset, int nbytes, unsigned int flags)
+
+def sync_file_range_test(int x):
+    print("sync_file_range exists\n")
+    if x==-1:
+        sync_file_range(1,1,1,1)
+    
+
+

sync_file_range_test/test.sh

@@ -0,0 +1,5 @@
+cd ../sync_file_range_test/
+python setup.py build_ext --inplace > setup.log 2> setup.err
+python sync_file_range_test.py > test.log 2> test.err
+grep "sync_file_range not existent" test.err | tail -n 1 | wc -l
+