checkout: Don't hardlink zero sized files

Alternative to https://github.com/ostreedev/ostree/pull/2197

Python's (usually) zero-sized `__init__.py` files can provoke
us hitting the hardlink limits on some filesystems (`EMLINK`).
At least one Fedora rpm-ostree user hit this.

The benefits of hardlinking here are quite marginal; lots
of hardlinks can behave suboptimally in particular filesystems
like BTRFS too.

This builds on prior code which made this an option, introduced
in 673cacd633
Now we just do it uncondtionally.

Also this provoked a different bug in a very obscure user mode checkout
case; when the "real" permissions were different from the "physical"
permissions, we would still hardlink.  Fix the test case for this.

man/ostree-checkout.xml

@@ -163,7 +163,7 @@ Boston, MA 02111-1307, USA.
                 <option>-z</option></term>
 
                 <listitem><para>
-                    Do not hardlink zero-sized files.
+                    This option does nothing; the functionality is now always on by default.
                 </para></listitem>
             </varlistentry>
 

src/libostree/ostree-repo-checkout.c

@@ -637,8 +637,12 @@ checkout_one_file_at (OstreeRepo                        *repo,
 
       need_copy = FALSE;
     }
-  else if ((options->force_copy_zerosized && is_reg_zerosized) || override_user_unreadable)
+  else if (is_reg_zerosized || override_user_unreadable)
     {
+      /* In https://github.com/ostreedev/ostree/commit/673cacd633f9d6b653cdea530657d3e780a41bbd we
+       * made this an option, but in order to avoid hitting EMLINK, we now force copy zerosized
+       * files unconditionally.
+       */
       need_copy = TRUE;
     }
   else if (!options->force_copy)

src/ostree/ot-builtin-checkout.c

@@ -84,7 +84,7 @@ static GOptionEntry options[] = {
   { "from-file", 0, 0, G_OPTION_ARG_STRING, &opt_from_file, "Process many checkouts from input file", "FILE" },
   { "fsync", 0, 0, G_OPTION_ARG_CALLBACK, parse_fsync_cb, "Specify how to invoke fsync()", "POLICY" },
   { "require-hardlinks", 'H', 0, G_OPTION_ARG_NONE, &opt_require_hardlinks, "Do not fall back to full copies if hardlinking fails", NULL },
-  { "force-copy-zerosized", 'z', 0, G_OPTION_ARG_NONE, &opt_force_copy_zerosized, "Do not hardlink zero-sized files", NULL },
+  { "force-copy-zerosized", 'z', G_OPTION_FLAG_HIDDEN, G_OPTION_ARG_NONE, &opt_force_copy_zerosized, "Do not hardlink zero-sized files", NULL },
   { "force-copy", 'C', 0, G_OPTION_ARG_NONE, &opt_force_copy, "Never hardlink (but may reflink if available)", NULL },
   { "bareuseronly-dirs", 'M', 0, G_OPTION_ARG_NONE, &opt_bareuseronly_dirs, "Suppress mode bits outside of 0775 for directories (suid, world writable, etc.)", NULL },
   { "skip-list", 0, 0, G_OPTION_ARG_FILENAME, &opt_skiplist_file, "File containing list of files to skip", "FILE" },

tests/basic-test.sh

@@ -750,15 +750,17 @@ rm files -rf && mkdir files
 touch files/anemptyfile
 touch files/anotheremptyfile
 $CMD_PREFIX ostree --repo=repo commit --consume -b tree-with-empty-files --tree=dir=files
+$CMD_PREFIX ostree --repo=repo checkout ${CHECKOUT_H_ARGS} tree-with-empty-files tree-with-empty-files
+if files_are_hardlinked tree-with-empty-files/an{,other}emptyfile; then
+    fatal "--force-copy-zerosized failed"
+fi
+# And pass the now-defunct -z option to validate it does nothing
+rm tree-with-empty-files -rf
 $CMD_PREFIX ostree --repo=repo checkout ${CHECKOUT_H_ARGS} -z tree-with-empty-files tree-with-empty-files
 if files_are_hardlinked tree-with-empty-files/an{,other}emptyfile; then
     fatal "--force-copy-zerosized failed"
 fi
-rm tree-with-empty-files -rf
-$CMD_PREFIX ostree --repo=repo checkout ${CHECKOUT_H_ARGS} tree-with-empty-files tree-with-empty-files
-assert_files_hardlinked tree-with-empty-files/an{,other}emptyfile
-rm tree-with-empty-files -rf
-echo "ok checkout --force-copy-zerosized"
+echo "ok checkout zero sized files are not hardlinked"
 
 # These should merge, they're identical
 $CMD_PREFIX ostree --repo=repo checkout ${CHECKOUT_H_ARGS} --union-identical -z tree-with-empty-files tree-with-empty-files

tests/test-libarchive.sh

@@ -37,7 +37,7 @@ mkdir foo
 cd foo
 mkdir -p usr/bin usr/lib
 echo contents > usr/bin/foo
-touch usr/bin/foo0
+echo foo0 > usr/bin/foo0
 ln usr/bin/foo usr/bin/bar
 ln usr/bin/foo0 usr/bin/bar0
 ln -s foo usr/bin/sl
@@ -45,8 +45,8 @@ mkdir -p usr/local/bin
 ln usr/bin/foo usr/local/bin/baz
 ln usr/bin/foo0 usr/local/bin/baz0
 ln usr/bin/sl usr/local/bin/slhl
-touch usr/bin/setuidme
-touch usr/bin/skipme
+echo setuidme > usr/bin/setuidme
+echo skipme > usr/bin/skipme
 echo "a library" > usr/lib/libfoo.so
 echo "another library" > usr/lib/libbar.so
 
@@ -102,9 +102,9 @@ assert_valid_content () {
   assert_file_has_content usr/bin/foo contents
   assert_file_has_content usr/bin/bar contents
   assert_file_has_content usr/local/bin/baz contents
-  assert_file_empty usr/bin/foo0
-  assert_file_empty usr/bin/bar0
-  assert_file_empty usr/local/bin/baz0
+  assert_file_has_content usr/bin/foo0 foo0
+  assert_file_has_content usr/bin/bar0 foo0
+  assert_file_has_content usr/local/bin/baz0 foo0
   assert_file_has_content usr/lib/libfoo.so 'a library'
   assert_file_has_content usr/lib/libbar.so 'another library'
 
@@ -244,7 +244,7 @@ ${CMD_PREFIX} ostree --repo=repo2 commit \
   --generate-sizes \
   --tree=tar=foo.tar.gz
 ${CMD_PREFIX} ostree --repo=repo2 show --print-sizes test-tar > sizes.txt
-assert_file_has_content sizes.txt 'Compressed size (needed/total): 0[  ]bytes/1.1[  ]kB'
-assert_file_has_content sizes.txt 'Unpacked size (needed/total): 0[  ]bytes/900[  ]bytes'
-assert_file_has_content sizes.txt 'Number of objects (needed/total): 0/12'
+assert_file_has_content sizes.txt 'Compressed size (needed/total): 0[  ]bytes/1.2[  ]kB'
+assert_file_has_content sizes.txt 'Unpacked size (needed/total): 0[  ]bytes/921[  ]bytes'
+assert_file_has_content sizes.txt 'Number of objects (needed/total): 0/14'
 echo "ok tar sizes metadata"