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OSTree: Allow support FAT boot filesystem
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Systemd boot requires the boot partition to be the EFI partition which
means FAT is required. OSTree uses symlinking as a way to do atomic
update.

There is no solution yet for atomic update of FAT partitions. THis
patch however changes symlinking by doing directory move which can be
atomic in conditions. In practice filesystems with symbolic link
support usually also support atomic rename of directories. But this
allows to also work when no atomic update is working.

Patch was submitted upstream as
ostreedev/ostree#1967
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valentindavid committed Jan 13, 2020
1 parent 9d6fdbd commit 2ffd7aa
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2 changes: 2 additions & 0 deletions elements/core-deps/ostree.bst
Original file line number Diff line number Diff line change
Expand Up @@ -3,6 +3,8 @@ kind: autotools
sources:
- kind: tar
url: github_com:ostreedev/ostree/releases/download/v2019.5/libostree-2019.5.tar.xz
- kind: patch
path: files/ostree/no-boot-symlink.patch

build-depends:
- sdk/gobject-introspection.bst
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313 changes: 313 additions & 0 deletions files/ostree/no-boot-symlink.patch
Original file line number Diff line number Diff line change
@@ -0,0 +1,313 @@
diff --git a/src/libostree/ostree-sysroot-cleanup.c b/src/libostree/ostree-sysroot-cleanup.c
index ef95d13c..33756f7d 100644
--- a/src/libostree/ostree-sysroot-cleanup.c
+++ b/src/libostree/ostree-sysroot-cleanup.c
@@ -216,6 +216,15 @@ cleanup_other_bootversions (OstreeSysroot *self,
const int cleanup_subbootversion = self->subbootversion == 0 ? 1 : 0;
/* Reusable buffer for path */
g_autoptr(GString) buf = g_string_new ("");
+ struct stat stbuf;
+
+ if ((glnx_fstatat_allow_noent (self->sysroot_fd, "boot/loader", &stbuf, AT_SYMLINK_NOFOLLOW, error))
+ && (!S_ISLNK (stbuf.st_mode)))
+ {
+ g_string_truncate (buf, 0); g_string_append_printf (buf, "boot/loader.%d", self->bootversion);
+ if (!glnx_shutil_rm_rf_at (self->sysroot_fd, buf->str, cancellable, error))
+ return FALSE;
+ }

/* These directories are for the other major version */
g_string_truncate (buf, 0); g_string_append_printf (buf, "boot/loader.%d", cleanup_bootversion);
diff --git a/src/libostree/ostree-sysroot-deploy.c b/src/libostree/ostree-sysroot-deploy.c
index a09c354b..8a32e090 100644
--- a/src/libostree/ostree-sysroot-deploy.c
+++ b/src/libostree/ostree-sysroot-deploy.c
@@ -1829,38 +1829,89 @@ install_deployment_kernel (OstreeSysroot *sysroot,
return TRUE;
}

-/* We generate the symlink on disk, then potentially do a syncfs() to ensure
- * that it (and everything else we wrote) has hit disk. Only after that do we
- * rename it into place.
- */
static gboolean
-prepare_new_bootloader_link (OstreeSysroot *sysroot,
- int current_bootversion,
- int new_bootversion,
- GCancellable *cancellable,
- GError **error)
+prepare_new_bootloader_dir (OstreeSysroot *sysroot,
+ int current_bootversion,
+ int new_bootversion,
+ GCancellable *cancellable,
+ GError **error)
{
- GLNX_AUTO_PREFIX_ERROR ("Preparing final bootloader swap", error);
+ glnx_autofd int boot_dfd = -1;
+
+ GLNX_AUTO_PREFIX_ERROR ("Preparing new bootloader directory", error);
g_assert ((current_bootversion == 0 && new_bootversion == 1) ||
(current_bootversion == 1 && new_bootversion == 0));

- g_autofree char *new_target = g_strdup_printf ("loader.%d", new_bootversion);
+ if (!glnx_opendirat (sysroot->sysroot_fd, "boot", TRUE, &boot_dfd, error))
+ return FALSE;

- /* We shouldn't actually need to replace but it's easier to reuse
- that code */
- if (!symlink_at_replace (new_target, sysroot->sysroot_fd, "boot/loader.tmp",
- cancellable, error))
+ g_autofree char *loader_dir_name = g_strdup_printf ("loader.%d", new_bootversion);
+
+ if (!glnx_shutil_mkdir_p_at (boot_dfd, loader_dir_name, 0755,
+ cancellable, error))
+ return FALSE;
+
+ g_autofree char *version_name = g_strdup_printf ("%s/version", loader_dir_name);
+
+ if (!glnx_file_replace_contents_at (boot_dfd, version_name,
+ (guint8*)loader_dir_name, strlen(loader_dir_name),
+ 0, cancellable, error))
return FALSE;

return TRUE;
}

+static gboolean
+renameat2_exchange (int olddirfd,
+ const char *oldpath,
+ int newdirfd,
+ const char *newpath,
+ gboolean *is_atomic,
+ GError **error)
+{
+ if (renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_EXCHANGE) == 0)
+ return TRUE;
+ else
+ {
+ if ((errno == EINVAL)
+ || (errno == ENOSYS))
+ {
+ if (glnx_renameat2_exchange (olddirfd, oldpath, newdirfd, newpath) == 0)
+ {
+ is_atomic = FALSE;
+ return TRUE;
+ }
+ }
+ }
+
+ if (errno != ENOENT)
+ return glnx_throw_errno_prefix (error, "renameat2");
+
+ if (renameat2(olddirfd, oldpath, newdirfd, newpath, RENAME_NOREPLACE) == 0)
+ return TRUE;
+ else
+ {
+ if ((errno == EINVAL)
+ || (errno == ENOSYS))
+ {
+ if (glnx_renameat2_noreplace (olddirfd, oldpath, newdirfd, newpath) == 0)
+ {
+ is_atomic = FALSE;
+ return TRUE;
+ }
+ }
+ }
+
+ return glnx_throw_errno_prefix (error, "renameat2");
+}
+
/* Update the /boot/loader symlink to point to /boot/loader.$new_bootversion */
static gboolean
swap_bootloader (OstreeSysroot *sysroot,
OstreeBootloader *bootloader,
int current_bootversion,
int new_bootversion,
+ gboolean *is_atomic,
GCancellable *cancellable,
GError **error)
{
@@ -1873,11 +1924,8 @@ swap_bootloader (OstreeSysroot *sysroot,
if (!glnx_opendirat (sysroot->sysroot_fd, "boot", TRUE, &boot_dfd, error))
return FALSE;

- /* The symlink was already written, and we used syncfs() to ensure
- * its data is in place. Renaming now should give us atomic semantics;
- * see https://bugzilla.gnome.org/show_bug.cgi?id=755595
- */
- if (!glnx_renameat (boot_dfd, "loader.tmp", boot_dfd, "loader", error))
+ g_autofree char *new_target = g_strdup_printf ("loader.%d", new_bootversion);
+ if (!renameat2_exchange(boot_dfd, new_target, boot_dfd, "loader", is_atomic, error))
return FALSE;

/* Now we explicitly fsync this directory, even though it
@@ -2098,6 +2146,7 @@ write_deployments_bootswap (OstreeSysroot *self,
OstreeSysrootWriteDeploymentsOpts *opts,
OstreeBootloader *bootloader,
SyncStats *out_syncstats,
+ gboolean *is_atomic,
GCancellable *cancellable,
GError **error)
{
@@ -2160,15 +2209,16 @@ write_deployments_bootswap (OstreeSysroot *self,
return glnx_prefix_error (error, "Bootloader write config");
}

- if (!prepare_new_bootloader_link (self, self->bootversion, new_bootversion,
- cancellable, error))
+ if (!prepare_new_bootloader_dir (self, self->bootversion, new_bootversion,
+ cancellable, error))
return FALSE;

if (!full_system_sync (self, out_syncstats, cancellable, error))
return FALSE;

if (!swap_bootloader (self, bootloader, self->bootversion, new_bootversion,
- cancellable, error))
+ is_atomic, cancellable, error))
+
return FALSE;

return TRUE;
@@ -2407,7 +2457,8 @@ ostree_sysroot_write_deployments_with_options (OstreeSysroot *self,

/* Note equivalent of try/finally here */
gboolean success = write_deployments_bootswap (self, new_deployments, opts, bootloader,
- &syncstats, cancellable, error);
+ &syncstats, &bootloader_is_atomic,
+ cancellable, error);
/* Below here don't set GError until the if (!success) check */
if (boot_was_ro_mount)
{
diff --git a/src/libostree/ostree-sysroot.c b/src/libostree/ostree-sysroot.c
index 1c9dbf37..5973db1f 100644
--- a/src/libostree/ostree-sysroot.c
+++ b/src/libostree/ostree-sysroot.c
@@ -432,6 +432,60 @@ compare_loader_configs_for_sorting (gconstpointer a_pp,
return compare_boot_loader_configs (a, b);
}

+static gboolean
+read_current_bootversion (OstreeSysroot *self,
+ int *out_bootversion,
+ GCancellable *cancellable,
+ GError **error)
+{
+ int ret_bootversion;
+ struct stat stbuf;
+
+ if (!glnx_fstatat_allow_noent (self->sysroot_fd, "boot/loader", &stbuf, AT_SYMLINK_NOFOLLOW, error))
+ return FALSE;
+ if (errno == ENOENT)
+ {
+ ret_bootversion = 0;
+ }
+ else
+ {
+ if (!S_ISLNK (stbuf.st_mode))
+ {
+ gsize len;
+ g_autofree char* version_content = glnx_file_get_contents_utf8_at(self->sysroot_fd, "boot/loader/version",
+ &len, cancellable, error);
+ if (version_content == NULL) {
+ return FALSE;
+ }
+ if (len != 8)
+ return glnx_throw (error, "Invalid version in boot/loader/version");
+ else if (g_strcmp0 (version_content, "loader.0") == 0)
+ ret_bootversion = 0;
+ else if (g_strcmp0 (version_content, "loader.1") == 0)
+ ret_bootversion = 1;
+ else
+ return glnx_throw (error, "Invalid version in boot/loader/version");
+ }
+ else
+ {
+ /* Backward compatibility with boot symbolic links */
+ g_autofree char *target =
+ glnx_readlinkat_malloc (self->sysroot_fd, "boot/loader", cancellable, error);
+ if (!target)
+ return FALSE;
+ if (g_strcmp0 (target, "loader.0") == 0)
+ ret_bootversion = 0;
+ else if (g_strcmp0 (target, "loader.1") == 0)
+ ret_bootversion = 1;
+ else
+ return glnx_throw (error, "Invalid target '%s' in boot/loader", target);
+ }
+ }
+
+ *out_bootversion = ret_bootversion;
+ return TRUE;
+}
+
gboolean
_ostree_sysroot_read_boot_loader_configs (OstreeSysroot *self,
int bootversion,
@@ -445,12 +499,22 @@ _ostree_sysroot_read_boot_loader_configs (OstreeSysroot *self,
g_autoptr(GPtrArray) ret_loader_configs =
g_ptr_array_new_with_free_func ((GDestroyNotify)g_object_unref);

- g_autofree char *entries_path = g_strdup_printf ("boot/loader.%d/entries", bootversion);
+ g_autofree char *entries_path = NULL;
+ int current_version;
+ if (!read_current_bootversion (self, &current_version, cancellable, error))
+ return FALSE;
+
+ if (current_version == bootversion)
+ entries_path = g_strdup ("boot/loader/entries");
+ else
+ entries_path = g_strdup_printf ("boot/loader.%d/entries", bootversion);
+
gboolean entries_exists;
g_auto(GLnxDirFdIterator) dfd_iter = { 0, };
if (!ot_dfd_iter_init_allow_noent (self->sysroot_fd, entries_path,
&dfd_iter, &entries_exists, error))
return FALSE;
+
if (!entries_exists)
{
/* Note early return */
@@ -490,42 +554,6 @@ _ostree_sysroot_read_boot_loader_configs (OstreeSysroot *self,
return TRUE;
}

-static gboolean
-read_current_bootversion (OstreeSysroot *self,
- int *out_bootversion,
- GCancellable *cancellable,
- GError **error)
-{
- int ret_bootversion;
- struct stat stbuf;
-
- if (!glnx_fstatat_allow_noent (self->sysroot_fd, "boot/loader", &stbuf, AT_SYMLINK_NOFOLLOW, error))
- return FALSE;
- if (errno == ENOENT)
- {
- ret_bootversion = 0;
- }
- else
- {
- if (!S_ISLNK (stbuf.st_mode))
- return glnx_throw (error, "Not a symbolic link: boot/loader");
-
- g_autofree char *target =
- glnx_readlinkat_malloc (self->sysroot_fd, "boot/loader", cancellable, error);
- if (!target)
- return FALSE;
- if (g_strcmp0 (target, "loader.0") == 0)
- ret_bootversion = 0;
- else if (g_strcmp0 (target, "loader.1") == 0)
- ret_bootversion = 1;
- else
- return glnx_throw (error, "Invalid target '%s' in boot/loader", target);
- }
-
- *out_bootversion = ret_bootversion;
- return TRUE;
-}
-
static gboolean
load_origin (OstreeSysroot *self,
OstreeDeployment *deployment,

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