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[RFC] sysroot: Support for directories instead of symbolic links in boot part #3359

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[RFC] sysroot: Support for directories instead of symbolic links in boot part #3359

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117 changes: 107 additions & 10 deletions src/libostree/ostree-sysroot-deploy.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2212,10 +2212,60 @@ prepare_new_bootloader_link (OstreeSysroot *sysroot, int current_bootversion, in
return TRUE;
}

/* We generate the directory 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 (via renameat2 RENAME_EXCHANGE).
*/
static gboolean
prepare_new_bootloader_dir (OstreeSysroot *sysroot,
int current_bootversion,
int new_bootversion,
GCancellable *cancellable,
GError **error)
{
GLNX_AUTO_PREFIX_ERROR ("Preparing bootloader directory", error);
g_assert ((current_bootversion == 0 && new_bootversion == 1) ||
(current_bootversion == 1 && new_bootversion == 0));

if (!_ostree_sysroot_ensure_boot_fd (sysroot, error))
return FALSE;

/* This allows us to support both /boot on a seperate filesystem to / as well
* as on the same filesystem. Allowed to fail with EPERM on ESP/vfat.
*/
if (TEMP_FAILURE_RETRY (symlinkat (".", sysroot->sysroot_fd, "boot/boot")) < 0)
if (errno != EPERM && errno != EEXIST)
return glnx_throw_errno_prefix (error, "symlinkat");
Comment on lines +2236 to +2238
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This is the bit I'd like to have dispatch on the srel file in particular.

To be conformant, we shouldn't create a symlink even if we can - the spec just says that XBOOTLDR needs to be something "the firmware" can read, and maybe someone makes a firmware that handles ext4 or whatever.

To be clear there's no good reason I am aware of to make XBOOTLDR something other than VFAT today - but still, the srel file seems like the right way to dispatch.

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Oh and as a big bonus, dispatching on that file means we can unit test this code without setting up a special hack to make symlink writing fail with EPERM etc.


/* As the directory gets swapped with glnx_renameat2_exchange, the new bootloader
* deployment needs to first be moved to the 'old' path, as the 'current' one will
* become the older deployment after the exchange.
*/
g_autofree char *loader_new = g_strdup_printf ("loader.%d", new_bootversion);
g_autofree char *loader_old = g_strdup_printf ("loader.%d", current_bootversion);

/* Tag boot version under an ostree specific file */
g_autofree char *version_name = g_strdup_printf ("%s/ostree_bootversion", loader_new);
if (!glnx_file_replace_contents_at (sysroot->boot_fd, version_name,
(guint8*)loader_new, strlen(loader_new),
0, cancellable, error))
return FALSE;

/* It is safe to remove older loader version as it wasn't really deployed */
if (!glnx_shutil_rm_rf_at (sysroot->boot_fd, loader_old, cancellable, error))
return FALSE;

/* Rename new deployment to the older path before the exchange */
if (!glnx_renameat2_noreplace (sysroot->boot_fd, loader_new, sysroot->boot_fd, loader_old))
return FALSE;

return TRUE;
}

/* 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, GCancellable *cancellable, GError **error)
swap_bootloader (OstreeSysroot *sysroot, OstreeBootloader *bootloader, gboolean loader_link,
int current_bootversion, int new_bootversion, GCancellable *cancellable, GError **error)
{
GLNX_AUTO_PREFIX_ERROR ("Final bootloader swap", error);

Expand All @@ -2225,12 +2275,22 @@ swap_bootloader (OstreeSysroot *sysroot, OstreeBootloader *bootloader, int curre
if (!_ostree_sysroot_ensure_boot_fd (sysroot, 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 (sysroot->boot_fd, "loader.tmp", sysroot->boot_fd, "loader", error))
return FALSE;
if (loader_link)
{
/* 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 (sysroot->boot_fd, "loader.tmp", sysroot->boot_fd, "loader", error))
return FALSE;
}
else
{
/* New target is currently under the old/current version */
g_autofree char *new_target = g_strdup_printf ("loader.%d", current_bootversion);
if (glnx_renameat2_exchange (sysroot->boot_fd, new_target, sysroot->boot_fd, "loader") != 0)
return FALSE;
}

/* Now we explicitly fsync this directory, even though it
* isn't required for atomicity, for two reasons:
Expand Down Expand Up @@ -2448,13 +2508,50 @@ write_deployments_bootswap (OstreeSysroot *self, GPtrArray *new_deployments,
return glnx_prefix_error (error, "Bootloader write config");
}

if (!prepare_new_bootloader_link (self, self->bootversion, new_bootversion, cancellable, error))
/* Handle when boot/loader is a link (normal deployment) and as a normal directory (e.g. EFI/vfat) */
struct stat stbuf;
gboolean loader_link = FALSE;
if (!glnx_fstatat_allow_noent (self->sysroot_fd, "boot/loader", &stbuf, AT_SYMLINK_NOFOLLOW, error))
return FALSE;
if (errno == ENOENT)
{
/* When there is no loader, check if the fs supports symlink or not */
if (TEMP_FAILURE_RETRY (symlinkat (".", self->sysroot_fd, "boot/boot")) < 0)
{
if (errno == EPERM)
loader_link = FALSE;
else if (errno != EEXIST)
return glnx_throw_errno_prefix (error, "symlinkat");
}
else
loader_link = TRUE;
}
else if (S_ISLNK (stbuf.st_mode))
loader_link = TRUE;
else if (S_ISDIR (stbuf.st_mode))
loader_link = FALSE;
else
return FALSE;

if (loader_link)
{
/* Default and when loader is a link is to swap links */
if (!prepare_new_bootloader_link (self, self->bootversion, new_bootversion,
cancellable, error))
return FALSE;
}
else
{
/* Handle boot/loader as a directory, and swap with renameat2 RENAME_EXCHANGE */
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))
if (!swap_bootloader (self, bootloader, loader_link, self->bootversion, new_bootversion, cancellable, error))
return FALSE;

if (out_subbootdir)
Expand Down
65 changes: 50 additions & 15 deletions src/libostree/ostree-sysroot.c
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Original file line number Diff line number Diff line change
Expand Up @@ -601,6 +601,12 @@ compare_loader_configs_for_sorting (gconstpointer a_pp, gconstpointer b_pp)
return compare_boot_loader_configs (a, b);
}

static gboolean
read_current_bootversion (OstreeSysroot *self,
int *out_bootversion,
GCancellable *cancellable,
GError **error);

/* Read all the bootconfigs from `/boot/loader/`. */
gboolean
_ostree_sysroot_read_boot_loader_configs (OstreeSysroot *self, int bootversion,
Expand All @@ -613,7 +619,16 @@ _ostree_sysroot_read_boot_loader_configs (OstreeSysroot *self, int bootversion,
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,
Expand Down Expand Up @@ -660,7 +675,7 @@ _ostree_sysroot_read_boot_loader_configs (OstreeSysroot *self, int bootversion,
return TRUE;
}

/* Get the bootversion from the `/boot/loader` symlink. */
/* Get the bootversion from the `/boot/loader` directory or symlink. */
static gboolean
read_current_bootversion (OstreeSysroot *self, int *out_bootversion, GCancellable *cancellable,
GError **error)
Expand All @@ -673,24 +688,44 @@ read_current_bootversion (OstreeSysroot *self, int *out_bootversion, GCancellabl
return FALSE;
if (errno == ENOENT)
{
g_debug ("Didn't find $sysroot/boot/loader symlink; assuming bootversion 0");
g_debug ("Didn't find $sysroot/boot/loader directory or symlink; assuming bootversion 0");
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;
if (S_ISLNK (stbuf.st_mode))
{
/* Traditional link, check version by reading link name */
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);
}
else
return glnx_throw (error, "Invalid target '%s' in boot/loader", target);
{
/* Loader is a directory, check version by reading ostree_bootversion */
gsize len;
g_autofree char* version =
glnx_file_get_contents_utf8_at(self->sysroot_fd, "boot/loader/ostree_bootversion",
&len, cancellable, error);
if (version == NULL)
{
g_debug ("Invalid boot/loader/ostree_bootversion, assuming bootversion 0");
ret_bootversion = 0;
}
else if (g_strcmp0 (version, "loader.0") == 0)
ret_bootversion = 0;
else if (g_strcmp0 (version, "loader.1") == 0)
ret_bootversion = 1;
else
return glnx_throw (error, "Invalid version '%s' in boot/loader/ostree_bootversion", version);
}
}

*out_bootversion = ret_bootversion;
Expand Down
2 changes: 1 addition & 1 deletion src/switchroot/ostree-prepare-root.c
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Original file line number Diff line number Diff line change
Expand Up @@ -515,7 +515,7 @@ main (int argc, char *argv[])
* at /boot inside the deployment. */
if (snprintf (srcpath, sizeof (srcpath), "%s/boot/loader", root_mountpoint) < 0)
err (EXIT_FAILURE, "failed to assemble /boot/loader path");
if (lstat (srcpath, &stbuf) == 0 && S_ISLNK (stbuf.st_mode))
if (lstat (srcpath, &stbuf) == 0 && (S_ISLNK (stbuf.st_mode) || S_ISDIR (stbuf.st_mode)))
{
if (lstat ("boot", &stbuf) == 0 && S_ISDIR (stbuf.st_mode))
{
Expand Down
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