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krun: Parse libkrun flavor indicated in KRUN_VM_FILE #1754

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Merged
giuseppe merged 3 commits into from
May 22, 2025
Merged

krun: Parse libkrun flavor indicated in KRUN_VM_FILE #1754

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13fcca9
krun: Add function to parse krun VM config
tylerfanelli May 20, 2025
7d1d15d
krun: Configure VM with pre-parsed config tree
tylerfanelli May 21, 2025
379524f
krun: Determine flavor from VM config tree
tylerfanelli May 22, 2025
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129 changes: 93 additions & 36 deletions src/libcrun/handlers/krun.c
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Original file line number Diff line number Diff line change
Expand Up @@ -59,6 +59,8 @@
*/
#define KRUN_VM_FILE "/.krun_vm.json"

#define KRUN_FLAVOR_SEV "sev"

struct krun_config
{
void *handle;
Expand Down Expand Up @@ -138,17 +140,11 @@ libkrun_configure_kernel (uint32_t ctx_id, void *handle, yajl_val *config_tree,
}

static int
libkrun_configure_vm (uint32_t ctx_id, void *handle, bool *configured, libcrun_error_t *err)
libkrun_read_vm_config (yajl_val *config_tree, libcrun_error_t *err)
{
int32_t (*krun_set_vm_config) (uint32_t ctx_id, uint8_t num_vcpus, uint32_t ram_mib);
struct parser_context ctx = { 0, stderr };
cleanup_free char *config = NULL;
yajl_val config_tree = NULL;
yajl_val cpus = NULL;
yajl_val ram_mib = NULL;
const char *path_cpus[] = { "cpus", (const char *) 0 };
const char *path_ram_mib[] = { "ram_mib", (const char *) 0 };
int ret;
cleanup_free char *config = NULL;
struct parser_context ctx = { 0, stderr };

if (access (KRUN_VM_FILE, F_OK) != 0)
return 0;
Expand All @@ -157,20 +153,36 @@ libkrun_configure_vm (uint32_t ctx_id, void *handle, bool *configured, libcrun_e
if (UNLIKELY (ret < 0))
return ret;

ret = parse_json_file (&config_tree, config, &ctx, err);
ret = parse_json_file (config_tree, config, &ctx, err);
if (UNLIKELY (ret < 0))
return ret;

return 0;
}

static int
libkrun_configure_vm (uint32_t ctx_id, void *handle, bool *configured, yajl_val *config_tree, libcrun_error_t *err)
{
int32_t (*krun_set_vm_config) (uint32_t ctx_id, uint8_t num_vcpus, uint32_t ram_mib);
yajl_val cpus = NULL;
yajl_val ram_mib = NULL;
const char *path_cpus[] = { "cpus", (const char *) 0 };
const char *path_ram_mib[] = { "ram_mib", (const char *) 0 };
int ret;

if (*config_tree == NULL)
return 0;

/* Try to configure an external kernel. If the configuration file doesn't
* specify a kernel, libkrun automatically fall back to using libkrunfw,
* if the library is present and was loaded while creating the context.
*/
ret = libkrun_configure_kernel (ctx_id, handle, &config_tree, err);
ret = libkrun_configure_kernel (ctx_id, handle, config_tree, err);
if (UNLIKELY (ret))
return ret;

cpus = yajl_tree_get (config_tree, path_cpus, yajl_t_number);
ram_mib = yajl_tree_get (config_tree, path_ram_mib, yajl_t_number);
cpus = yajl_tree_get (*config_tree, path_cpus, yajl_t_number);
ram_mib = yajl_tree_get (*config_tree, path_ram_mib, yajl_t_number);
/* Both cpus and ram_mib must be present at the same time */
if (cpus == NULL || ram_mib == NULL || ! YAJL_IS_INTEGER (cpus) || ! YAJL_IS_INTEGER (ram_mib))
return 0;
Expand All @@ -189,6 +201,60 @@ libkrun_configure_vm (uint32_t ctx_id, void *handle, bool *configured, libcrun_e
return 0;
}

static int
libkrun_configure_flavor (void *cookie, yajl_val *config_tree, libcrun_error_t *err)
{
int ret, sev_indicated = 0;
const char *path_flavor[] = { "flavor", (const char *) 0 };
struct krun_config *kconf = (struct krun_config *) cookie;
yajl_val val_flavor = NULL;
char *flavor = NULL;

// Read if the SEV flavor was indicated in the krun VM config.
val_flavor = yajl_tree_get (*config_tree, path_flavor, yajl_t_string);
if (val_flavor != NULL && YAJL_IS_STRING (val_flavor))
{
flavor = YAJL_GET_STRING (val_flavor);

// The SEV flavor will be used if the krun VM config indicates to use SEV
// within the "flavor" field.
sev_indicated |= strcmp (flavor, KRUN_FLAVOR_SEV) == 0;
}

// To maintain backward compatibility, also use the SEV flavor if the
// KRUN_SEV_FILE was found.
sev_indicated |= access (KRUN_SEV_FILE, F_OK) == 0;

if (sev_indicated)
{
if (kconf->handle_sev == NULL)
error (EXIT_FAILURE, 0, "the container requires libkrun-sev but it's not available");

// We no longer need the libkrun handle.
ret = dlclose (kconf->handle);
if (UNLIKELY (ret != 0))
return crun_make_error (err, 0, "could not unload handle: `%s`", dlerror ());

kconf->handle = kconf->handle_sev;
kconf->ctx_id = kconf->ctx_id_sev;
kconf->sev = true;
}
else
{
if (kconf->handle == NULL)
error (EXIT_FAILURE, 0, "the container requires libkrun but it's not available");

// We no longer need the libkrun-sev handle.
ret = dlclose (kconf->handle_sev);
if (UNLIKELY (ret != 0))
return crun_make_error (err, 0, "could not unload handle: `%s`", dlerror ());

kconf->sev = false;
}

return 0;
}

static int
libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname, char *const argv[])
{
Expand All @@ -206,23 +272,18 @@ libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname
cpu_set_t set;
libcrun_error_t err;
bool configured = false;
yajl_val config_tree = NULL;
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@giuseppe giuseppe May 21, 2025

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when do we clean it up (yajl_tree_free (...))?

We exit early on errors so we don't really care in this case, but could we release it before krun_start_enter?

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@tylerfanelli tylerfanelli May 22, 2025 •
edited
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Thanks for pointing that out, I never did free config_tree. I've modified 13fcca9 to free config_tree before krun_start_enter.


if (access (KRUN_SEV_FILE, F_OK) == 0)
{
if (kconf->handle_sev == NULL)
error (EXIT_FAILURE, 0, "the container requires libkrun-sev but it's not available");
handle = kconf->handle_sev;
ctx_id = kconf->ctx_id_sev;
kconf->sev = true;
}
else
{
if (kconf->handle == NULL)
error (EXIT_FAILURE, 0, "the container requires libkrun but it's not available");
handle = kconf->handle;
ctx_id = kconf->ctx_id;
kconf->sev = false;
}
ret = libkrun_read_vm_config (&config_tree, &err);
if (UNLIKELY (ret < 0))
error (EXIT_FAILURE, -ret, "libkrun VM config exists, but unable to parse");

ret = libkrun_configure_flavor (cookie, &config_tree, &err);
if (UNLIKELY (ret < 0))
error (EXIT_FAILURE, -ret, "unable to configure libkrun flavor");

handle = kconf->handle;
ctx_id = kconf->ctx_id;

krun_set_log_level = dlsym (handle, "krun_set_log_level");
krun_start_enter = dlsym (handle, "krun_start_enter");
Expand Down Expand Up @@ -259,7 +320,7 @@ libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname
error (EXIT_FAILURE, -ret, "could not set krun root");
}

ret = libkrun_configure_vm (ctx_id, handle, &configured, &err);
ret = libkrun_configure_vm (ctx_id, handle, &configured, &config_tree, &err);
if (UNLIKELY (ret))
{
libcrun_error_t *tmp_err = &err;
Expand Down Expand Up @@ -295,6 +356,8 @@ libkrun_exec (void *cookie, libcrun_container_t *container, const char *pathname
error (EXIT_FAILURE, -ret, "could not set krun vm configuration");
}

yajl_tree_free (config_tree);

ret = krun_start_enter (ctx_id);
return -ret;
}
Expand Down Expand Up @@ -467,12 +530,6 @@ libkrun_unload (void *cookie, libcrun_error_t *err)
if (UNLIKELY (r != 0))
return crun_make_error (err, 0, "could not unload handle: `%s`", dlerror ());
}
if (kconf->handle_sev != NULL)
{
r = dlclose (kconf->handle_sev);
if (UNLIKELY (r != 0))
return crun_make_error (err, 0, "could not unload handle_sev: `%s`", dlerror ());
}
}
return 0;
}
Expand Down