From: Gabriel Somlo <somlo@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@cmu.edu> Cc: Andy Lutomirski <luto@amacapital.net> --- .../ABI/testing/sysfs-firmware-qemu_fw_cfg | 42 ++++++++ drivers/firmware/qemu_fw_cfg.c | 109 ++++++++++++++++++++- 2 files changed, 148 insertions(+), 3 deletions(-) diff --git a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg index b908b6d..a346ee0 100644 --- a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg +++ b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg @@ -196,3 +196,45 @@ 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 618304a..9ac1ca7 100644 --- a/drivers/firmware/qemu_fw_cfg.c +++ b/drivers/firmware/qemu_fw_cfg.c @@ -318,9 +318,103 @@ 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) @@ -347,6 +441,9 @@ 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; @@ -401,18 +498,21 @@ 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); @@ -441,6 +541,8 @@ 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; @@ -450,6 +552,7 @@ 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; -- 2.4.3