cmd/libsnap: add simplified feature flag checker #6116
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,86 @@ | ||
| /* | ||
| * Copyright (C) 2018 Canonical Ltd | ||
| * | ||
| * This program is free software: you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License version 3 as | ||
| * published by the Free Software Foundation. | ||
| * | ||
| * This program is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
| * | ||
| */ | ||
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| #include "feature.h" | ||
| #include "feature.c" | ||
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| #include <limits.h> | ||
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| #include <glib.h> | ||
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| #include "string-utils.h" | ||
| #include "test-utils.h" | ||
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| static char *sc_testdir(void) | ||
| { | ||
| char *d = g_dir_make_tmp(NULL, NULL); | ||
| g_assert_nonnull(d); | ||
| g_test_queue_free(d); | ||
| g_test_queue_destroy((GDestroyNotify) rm_rf_tmp, d); | ||
| return d; | ||
| } | ||
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| // Set the feature flag directory to given value, useful for cleanup handlers. | ||
| static void set_feature_flag_dir(const char *dir) | ||
| { | ||
| feature_flag_dir = dir; | ||
| } | ||
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| // Mock the location of the feature flag directory. | ||
| static void sc_mock_feature_flag_dir(const char *d) | ||
| { | ||
| g_test_queue_destroy((GDestroyNotify) set_feature_flag_dir, | ||
| (void *)feature_flag_dir); | ||
| set_feature_flag_dir(d); | ||
| } | ||
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| static void test_feature_enabled__missing_dir(void) | ||
| { | ||
| const char *d = sc_testdir(); | ||
| char subd[PATH_MAX]; | ||
| sc_must_snprintf(subd, sizeof subd, "%s/absent", d); | ||
| sc_mock_feature_flag_dir(subd); | ||
| g_assert(!sc_feature_enabled(SC_PER_USER_MOUNT_NAMESPACE)); | ||
| } | ||
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| static void test_feature_enabled__missing_file(void) | ||
| { | ||
| const char *d = sc_testdir(); | ||
| sc_mock_feature_flag_dir(d); | ||
| g_assert(!sc_feature_enabled(SC_PER_USER_MOUNT_NAMESPACE)); | ||
| } | ||
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| static void test_feature_enabled__present_file(void) | ||
| { | ||
| const char *d = sc_testdir(); | ||
| sc_mock_feature_flag_dir(d); | ||
| char pname[PATH_MAX]; | ||
| sc_must_snprintf(pname, sizeof pname, "%s/per-user-mount-namespace", d); | ||
| g_file_set_contents(pname, "", -1, NULL); | ||
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| g_assert(sc_feature_enabled(SC_PER_USER_MOUNT_NAMESPACE)); | ||
| } | ||
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| static void __attribute__ ((constructor)) init(void) | ||
| { | ||
| g_test_add_func("/feature/missing_dir", | ||
| test_feature_enabled__missing_dir); | ||
| g_test_add_func("/feature/missing_file", | ||
| test_feature_enabled__missing_file); | ||
| g_test_add_func("/feature/present_file", | ||
| test_feature_enabled__present_file); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,62 @@ | ||
| /* | ||
| * Copyright (C) 2018 Canonical Ltd | ||
| * | ||
| * This program is free software: you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License version 3 as | ||
| * published by the Free Software Foundation. | ||
| * | ||
| * This program is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
| * | ||
| */ | ||
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| #define _GNU_SOURCE | ||
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| #include "feature.h" | ||
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| #include <errno.h> | ||
| #include <fcntl.h> | ||
| #include <sys/stat.h> | ||
| #include <sys/types.h> | ||
| #include <unistd.h> | ||
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| #include "cleanup-funcs.h" | ||
| #include "utils.h" | ||
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| static const char *feature_flag_dir = "/var/lib/snapd/features"; | ||
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| bool sc_feature_enabled(sc_feature_flag flag) | ||
| { | ||
| const char *file_name; | ||
| switch (flag) { | ||
| case SC_PER_USER_MOUNT_NAMESPACE: | ||
| file_name = "per-user-mount-namespace"; | ||
| break; | ||
| default: | ||
| die("unknown feature flag code %d", flag); | ||
| } | ||
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| int dirfd SC_CLEANUP(sc_cleanup_close) = -1; | ||
| dirfd = open(feature_flag_dir, O_CLOEXEC | O_DIRECTORY | O_NOFOLLOW | O_PATH); | ||
| if (dirfd < 0 && errno == ENOENT) { | ||
| return false; | ||
| } | ||
| if (dirfd < 0) { | ||
| die("cannot open path %s", feature_flag_dir); | ||
| } | ||
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| struct stat file_info; | ||
| if (fstatat(dirfd, file_name, &file_info, AT_SYMLINK_NOFOLLOW) < 0) { | ||
| if (errno == ENOENT) { | ||
| return false; | ||
| } | ||
| die("cannot inspect file %s/%s", feature_flag_dir, file_name); | ||
| } | ||
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| return S_ISREG(file_info.st_mode); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,35 @@ | ||
| /* | ||
| * Copyright (C) 2018 Canonical Ltd | ||
| * | ||
| * This program is free software: you can redistribute it and/or modify | ||
| * it under the terms of the GNU General Public License version 3 as | ||
| * published by the Free Software Foundation. | ||
| * | ||
| * This program is distributed in the hope that it will be useful, | ||
| * but WITHOUT ANY WARRANTY; without even the implied warranty of | ||
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | ||
| * GNU General Public License for more details. | ||
| * | ||
| * You should have received a copy of the GNU General Public License | ||
| * along with this program. If not, see <http://www.gnu.org/licenses/>. | ||
| * | ||
| */ | ||
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| #ifndef SNAP_CONFINE_FEATURE_H | ||
| #define SNAP_CONFINE_FEATURE_H | ||
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| #include <stdbool.h> | ||
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| typedef enum sc_feature_flag { | ||
| SC_PER_USER_MOUNT_NAMESPACE, | ||
| } sc_feature_flag; | ||
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| /** | ||
| * sc_feature_enabled returns true if a given feature flag has been activated | ||
| * by the user via "snap set core experimental.xxx=true". This is determined by | ||
| * testing the presence of a file in /var/lib/snapd/features/ that is named | ||
| * after the flag name. | ||
| **/ | ||
| bool sc_feature_enabled(sc_feature_flag flag); | ||
|
There was a problem hiding this comment. I wonder if it would make sense to simply pass feature names here that directly map to filenames under features directory (and we would have const char* constants for them). That way adding a new feature flag would reduce the scope of changes (no need to touch sc_feature_enabled). Not a biggie, just a question for consideration. There was a problem hiding this comment. I thought about this but I decided to use an enum instead. There are only so many feature flags and it is easier to cause a typo this way (because you can always pass a string manually). This has the advantage that the code knows the set of flags that exist so it cannot be fooled. |
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| #endif | ||
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If you change the PR maybe SC_FEATURE_PER_USER_MOUNT_NAMESPACE (i.e. prefix with SC_FEATURE_) but not really important.
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I like the SC_FEATURE idea. I'll change this in the next one.