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[Qemu-devel] [PATCH v6 3/4] firmware: create directory hierarchy for sys


From: Gabriel L. Somlo
Subject: [Qemu-devel] [PATCH v6 3/4] firmware: create directory hierarchy for sysfs fw_cfg entries
Date: Fri, 4 Dec 2015 10:29:05 -0500

From: Gabriel Somlo <address@hidden>

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 <address@hidden>
Cc: Andy Lutomirski <address@hidden>
---
 .../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 e9e58d4..011dda4 100644
--- a/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
+++ b/Documentation/ABI/testing/sysfs-firmware-qemu_fw_cfg
@@ -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.
diff --git a/drivers/firmware/qemu_fw_cfg.c b/drivers/firmware/qemu_fw_cfg.c
index 5b00d97..85f532a 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




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