[PATCH v2 3/3] firmware: fw_cfg: create directory hierarchy for fw_cfg file names
Gabriel L. Somlo
somlo at cmu.edu
Tue Aug 11 14:44:49 EDT 2015
From: "Gabriel Somlo" <somlo at cmu.edu>
Each fw_cfg entry of type "file" has an associated 56-char,
nul-terminated ASCII string which represents its name. While
the fw_cfg device doesn't itself impose any specific naming
convention, QEMU developers have traditionally used path name
semantics (i.e. "etc/acpi/rsdp") to descriptively name the
various fw_cfg "blobs" passed into the guest.
This patch attempts, on a best effort basis, to create a
directory hierarchy representing the content of fw_cfg file
names, under /sys/firmware/qemu_fw_cfg/by_name.
Upon successful creation of all directories representing the
"dirname" portion of a fw_cfg file, a symlink will be created
to represent the "basename", pointing at the appropriate
/sys/firmware/qemu_fw_cfg/by_key entry. If a file name is not
suitable for this procedure (e.g., if its basename or dirname
components collide with an already existing dirname component
or basename, respectively) the corresponding fw_cfg blob is
skipped and will remain available in sysfs only by its selector
key value.
Signed-off-by: Gabriel Somlo <somlo at cmu.edu>
---
.../ABI/testing/sysfs-firmware-qemu_fw_cfg | 42 +++++++++
drivers/firmware/qemu_fw_cfg.c | 104 +++++++++++++++++++++
2 files changed, 146 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
index 5bc2e3f..db0b10d 100644
--- a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
+++ b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
@@ -166,3 +166,45 @@ Description:
entry via the control register, and reading a number
of bytes equal to the blob size from the data
register.
+
+ --- Listing fw_cfg blobs by file name ---
+
+ While the fw_cfg device does not impose any specific naming
+ convention on the blobs registered in the file directory,
+ QEMU developers have traditionally used path name semantics
+ to give each blob a descriptive name. For example:
+
+ "bootorder"
+ "genroms/kvmvapic.bin"
+ "etc/e820"
+ "etc/boot-fail-wait"
+ "etc/system-states"
+ "etc/table-loader"
+ "etc/acpi/rsdp"
+ "etc/acpi/tables"
+ "etc/smbios/smbios-tables"
+ "etc/smbios/smbios-anchor"
+ ...
+
+ In addition to the listing by unique selector key described
+ above, the fw_cfg sysfs driver also attempts to build a tree
+ of directories matching the path name components of fw_cfg
+ blob names, ending in symlinks to the by_key entry for each
+ "basename", as illustrated below (assume current directory is
+ /sys/firmware):
+
+ qemu_fw_cfg/by_name/bootorder -> ../by_key/38
+ qemu_fw_cfg/by_name/etc/e820 -> ../../by_key/35
+ qemu_fw_cfg/by_name/etc/acpi/rsdp -> ../../../by_key/41
+ ...
+
+ Construction of the directory tree and symlinks is done on a
+ "best-effort" basis, as there is no guarantee that components
+ of fw_cfg blob names are always "well behaved". I.e., there is
+ the possibility that a symlink (basename) will conflict with
+ a dirname component of another fw_cfg blob, in which case the
+ creation of the offending /sys/firmware/qemu_fw_cfg/by_name
+ entry will be skipped.
+
+ The authoritative list of entries will continue to be found
+ under the /sys/firmware/qemu_fw_cfg/by_key directory.
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index cd26eee..b2fd222 100644
--- a/drivers/firmware/qemu_fw_cfg.c
+++ b/drivers/firmware/qemu_fw_cfg.c
@@ -345,9 +345,104 @@ static struct bin_attribute fw_cfg_sysfs_attr_raw = {
.read = fw_cfg_sysfs_read_raw,
};
+/*
+ * Create a kset subdirectory matching each '/' delimited dirname token
+ * in 'name', starting with sysfs kset/folder 'dir'; At the end, create
+ * a symlink directed at the given 'target'.
+ * NOTE: We do this on a best-effort basis, since 'name' is not guaranteed
+ * to be a well-behaved path name. Whenever a symlink vs. kset directory
+ * name collision occurs, the kernel will issue big scary warnings while
+ * refusing to add the offending link or directory. We follow up with our
+ * own, slightly less scary error messages explaining the situation :)
+ */
+static int __init fw_cfg_build_symlink(struct kset *dir,
+ struct kobject *target,
+ const char *name)
+{
+ int ret;
+ struct kset *subdir;
+ struct kobject *ko;
+ char *name_copy, *p, *tok;
+
+ if (!dir || !target || !name || !*name)
+ return -EINVAL;
+
+ /* clone a copy of name for parsing */
+ name_copy = p = kstrdup(name, GFP_KERNEL);
+ if (!name_copy)
+ return -ENOMEM;
+
+ /* create folders for each dirname token, then symlink for basename */
+ while ((tok = strsep(&p, "/")) && *tok) {
+
+ /* last (basename) token? If so, add symlink here */
+ if (!p || !*p) {
+ ret = sysfs_create_link(&dir->kobj, target, tok);
+ break;
+ }
+
+ /* does the current dir contain an item named after tok ? */
+ ko = kset_find_obj(dir, tok);
+ if (ko) {
+ /* drop reference added by kset_find_obj */
+ kobject_put(ko);
+
+ /* ko MUST be a kset - we're about to use it as one ! */
+ if (ko->ktype != dir->kobj.ktype) {
+ ret = -EINVAL;
+ break;
+ }
+
+ /* descend into already existing subdirectory */
+ dir = to_kset(ko);
+ } else {
+ /* create new subdirectory kset */
+ subdir = kzalloc(sizeof(struct kset), GFP_KERNEL);
+ if (!subdir) {
+ ret = -ENOMEM;
+ break;
+ }
+ subdir->kobj.kset = dir;
+ subdir->kobj.ktype = dir->kobj.ktype;
+ ret = kobject_set_name(&subdir->kobj, "%s", tok);
+ if (ret) {
+ kfree(subdir);
+ break;
+ }
+ ret = kset_register(subdir);
+ if (ret) {
+ kfree(subdir);
+ break;
+ }
+
+ /* descend into newly created subdirectory */
+ dir = subdir;
+ }
+ }
+
+ /* we're done with cloned copy of name */
+ kfree(name_copy);
+ return ret;
+}
+
+/* recursively unregister fw_cfg/by_name/ kset directory tree */
+static void fw_cfg_kset_unregister_recursive(struct kset *kset)
+{
+ struct kobject *k, *next;
+
+ list_for_each_entry_safe(k, next, &kset->list, entry)
+ /* all set members are ksets too, but check just in case... */
+ if (k->ktype == kset->kobj.ktype)
+ fw_cfg_kset_unregister_recursive(to_kset(k));
+
+ /* symlinks are cleanly and automatically removed with the directory */
+ kset_unregister(kset);
+}
+
/* kobjects & kset representing top-level, by_key, and by_name folders */
static struct kobject *fw_cfg_top_ko;
static struct kobject *fw_cfg_sel_ko;
+static struct kset *fw_cfg_fname_kset;
/* callback function to register an individual fw_cfg file */
static int __init fw_cfg_register_file(const struct fw_cfg_file *f)
@@ -376,6 +471,9 @@ static int __init fw_cfg_register_file(const struct fw_cfg_file *f)
if (err)
goto err_add_raw;
+ /* try adding "/sys/firmware/qemu_fw_cfg/by_name/" symlink */
+ fw_cfg_build_symlink(fw_cfg_fname_kset, &entry->kobj, entry->f.name);
+
/* success, add entry to global cache */
fw_cfg_sysfs_cache_enlist(entry);
return 0;
@@ -411,6 +509,9 @@ static int __init fw_cfg_sysfs_init(void)
fw_cfg_sel_ko = kobject_create_and_add("by_key", fw_cfg_top_ko);
if (!fw_cfg_sel_ko)
goto err_sel;
+ fw_cfg_fname_kset = kset_create_and_add("by_name", NULL, fw_cfg_top_ko);
+ if (!fw_cfg_fname_kset)
+ goto err_name;
/* get revision number, add matching top-level attribute */
fw_cfg_read_blob(FW_CFG_ID, &fw_cfg_rev, 0, sizeof(fw_cfg_rev));
@@ -432,6 +533,8 @@ err_scan:
fw_cfg_sysfs_cache_cleanup();
sysfs_remove_file(fw_cfg_top_ko, &fw_cfg_rev_attr.attr);
err_rev:
+ fw_cfg_kset_unregister_recursive(fw_cfg_fname_kset);
+err_name:
fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
err_sel:
fw_cfg_kobj_cleanup(fw_cfg_top_ko);
@@ -444,6 +547,7 @@ static void __exit fw_cfg_sysfs_exit(void)
{
pr_debug("fw_cfg: unloading.\n");
fw_cfg_sysfs_cache_cleanup();
+ fw_cfg_kset_unregister_recursive(fw_cfg_fname_kset);
fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
fw_cfg_kobj_cleanup(fw_cfg_top_ko);
fw_cfg_io_cleanup();
--
2.4.3
More information about the Kernelnewbies
mailing list