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firmware: create directory hierarchy for sysfs fw_cfg entries 

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@cmu.edu>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Gabriel Somlo 2016-01-28 09:23:13 -05:00 committed by Greg Kroah-Hartman
parent 75f3e8e47f
commit 246c46ebae
2 changed files with 148 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

42
Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
View File

@ -56,3 +56,45 @@ 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.

109
drivers/firmware/qemu_fw_cfg.c
View File

@ -334,9 +334,103 @@ static struct bin_attribute fw_cfg_sysfs_attr_raw = {
.read = fw_cfg_sysfs_read_raw,
};
/* kobjects representing top-level and by_key folders */
/*
* 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 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;
/* register an individual fw_cfg file */
static int fw_cfg_register_file(const struct fw_cfg_file *f)
@ -363,6 +457,9 @@ static int 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;
@ -417,18 +514,21 @@ static int fw_cfg_sysfs_probe(struct platform_device *pdev)
/* NOTE: If we supported multiple fw_cfg devices, we'd first create
* a subdirectory named after e.g. pdev->id, then hang per-device
* by_key subdirectories underneath it. However, only
* by_key (and by_name) subdirectories underneath it. However, only
* one fw_cfg device exist system-wide, so if one was already found
* earlier, we might as well stop here.
*/
if (fw_cfg_sel_ko)
return -EBUSY;
/* create by_key subdirectory of /sys/firmware/qemu_fw_cfg/ */
/* create by_key and by_name subdirs of /sys/firmware/qemu_fw_cfg/ */
err = -ENOMEM;
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;
/* initialize fw_cfg device i/o from platform data */
err = fw_cfg_do_platform_probe(pdev);
@ -457,6 +557,8 @@ err_dir:
err_rev:
fw_cfg_io_cleanup();
err_probe:
fw_cfg_kset_unregister_recursive(fw_cfg_fname_kset);
err_name:
fw_cfg_kobj_cleanup(fw_cfg_sel_ko);
err_sel:
return err;
@ -466,6 +568,7 @@ static int fw_cfg_sysfs_remove(struct platform_device *pdev)
{
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_io_cleanup();
return 0;