[PATCH v4 2/5] xen/hypfs: add support for id-based dynamic directories

[Juergen Gross <jgross@xxxxxxxx>]

Add some helpers to hypfs.c to support dynamic directories with a
numerical id as name.

The dynamic directory is based on a template specified by the user
allowing to use specific access functions and having a predefined
set of entries in the directory.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V2:
- use macro for length of entry name (Jan Beulich)
- const attributes (Jan Beulich)
- use template name as format string (Jan Beulich)
- add hypfs_dynid_entry_size() helper (Jan Beulich)
- expect dyndir data having been allocated by enter() callback

V3:
- add a specific enter() callback returning the template pointer
- add data field to struct hypfs_dyndir_id
- rename hypfs_gen_dyndir_entry_id() (Jan Beulich)
- add comments regarding generated names to be kept in sync (Jan Beulich)

V4:
- correct comments (Jan Beulich)
---
 xen/common/hypfs.c      | 98 +++++++++++++++++++++++++++++++++++++++++
 xen/include/xen/hypfs.h | 18 ++++++++
 2 files changed, 116 insertions(+)

diff --git a/xen/common/hypfs.c b/xen/common/hypfs.c
index 6c0e59dedd..5468497404 100644
--- a/xen/common/hypfs.c
+++ b/xen/common/hypfs.c
@@ -365,6 +365,104 @@ unsigned int hypfs_getsize(const struct hypfs_entry 
*entry)
     return entry->size;
 }
 
+/*
+ * Fill the direntry for a dynamically generated entry. Especially the
+ * generated name needs to be kept in sync with hypfs_gen_dyndir_id_entry().
+ */
+int hypfs_read_dyndir_id_entry(const struct hypfs_entry_dir *template,
+                               unsigned int id, bool is_last,
+                               XEN_GUEST_HANDLE_PARAM(void) *uaddr)
+{
+    struct xen_hypfs_dirlistentry direntry;
+    char name[HYPFS_DYNDIR_ID_NAMELEN];
+    unsigned int e_namelen, e_len;
+
+    e_namelen = snprintf(name, sizeof(name), template->e.name, id);
+    e_len = DIRENTRY_SIZE(e_namelen);
+    direntry.e.pad = 0;
+    direntry.e.type = template->e.type;
+    direntry.e.encoding = template->e.encoding;
+    direntry.e.content_len = template->e.funcs->getsize(&template->e);
+    direntry.e.max_write_len = template->e.max_size;
+    direntry.off_next = is_last ? 0 : e_len;
+    if ( copy_to_guest(*uaddr, &direntry, 1) )
+        return -EFAULT;
+    if ( copy_to_guest_offset(*uaddr, DIRENTRY_NAME_OFF, name,
+                              e_namelen + 1) )
+        return -EFAULT;
+
+    guest_handle_add_offset(*uaddr, e_len);
+
+    return 0;
+}
+
+static const struct hypfs_entry *hypfs_dyndir_enter(
+    const struct hypfs_entry *entry)
+{
+    const struct hypfs_dyndir_id *data;
+
+    data = hypfs_get_dyndata();
+
+    /* Use template with original enter function. */
+    return data->template->e.funcs->enter(&data->template->e);
+}
+
+static struct hypfs_entry *hypfs_dyndir_findentry(
+    const struct hypfs_entry_dir *dir, const char *name, unsigned int name_len)
+{
+    const struct hypfs_dyndir_id *data;
+
+    data = hypfs_get_dyndata();
+
+    /* Use template with original findentry function. */
+    return data->template->e.funcs->findentry(data->template, name, name_len);
+}
+
+static int hypfs_read_dyndir(const struct hypfs_entry *entry,
+                             XEN_GUEST_HANDLE_PARAM(void) uaddr)
+{
+    const struct hypfs_dyndir_id *data;
+
+    data = hypfs_get_dyndata();
+
+    /* Use template with original read function. */
+    return data->template->e.funcs->read(&data->template->e, uaddr);
+}
+
+/*
+ * Fill dyndata with a dynamically generated entry based on a template
+ * and a numerical id.
+ * Needs to be kept in sync with hypfs_read_dyndir_id_entry() regarding the
+ * name generated.
+ */
+struct hypfs_entry *hypfs_gen_dyndir_id_entry(
+    const struct hypfs_entry_dir *template, unsigned int id, void *data)
+{
+    struct hypfs_dyndir_id *dyndata;
+
+    dyndata = hypfs_get_dyndata();
+
+    dyndata->template = template;
+    dyndata->id = id;
+    dyndata->data = data;
+    snprintf(dyndata->name, sizeof(dyndata->name), template->e.name, id);
+    dyndata->dir = *template;
+    dyndata->dir.e.name = dyndata->name;
+    dyndata->dir.e.funcs = &dyndata->funcs;
+    dyndata->funcs = *template->e.funcs;
+    dyndata->funcs.enter = hypfs_dyndir_enter;
+    dyndata->funcs.findentry = hypfs_dyndir_findentry;
+    dyndata->funcs.read = hypfs_read_dyndir;
+
+    return &dyndata->dir.e;
+}
+
+unsigned int hypfs_dynid_entry_size(const struct hypfs_entry *template,
+                                    unsigned int id)
+{
+    return DIRENTRY_SIZE(snprintf(NULL, 0, template->name, id));
+}
+
 int hypfs_read_dir(const struct hypfs_entry *entry,
                    XEN_GUEST_HANDLE_PARAM(void) uaddr)
 {
diff --git a/xen/include/xen/hypfs.h b/xen/include/xen/hypfs.h
index d028c01283..e9d4c2555b 100644
--- a/xen/include/xen/hypfs.h
+++ b/xen/include/xen/hypfs.h
@@ -76,6 +76,17 @@ struct hypfs_entry_dir {
     struct list_head dirlist;
 };
 
+struct hypfs_dyndir_id {
+    struct hypfs_entry_dir dir;             /* Modified copy of template. */
+    struct hypfs_funcs funcs;               /* Dynamic functions. */
+    const struct hypfs_entry_dir *template; /* Template used. */
+#define HYPFS_DYNDIR_ID_NAMELEN 12
+    char name[HYPFS_DYNDIR_ID_NAMELEN];     /* Name of hypfs entry. */
+
+    unsigned int id;                        /* Numerical id. */
+    void *data;                             /* Data associated with id. */
+};
+
 #define HYPFS_DIR_INIT_FUNC(var, nam, fn)         \
     struct hypfs_entry_dir __read_mostly var = {  \
         .e.type = XEN_HYPFS_TYPE_DIR,             \
@@ -186,6 +197,13 @@ void *hypfs_alloc_dyndata(unsigned long size);
 #define hypfs_alloc_dyndata(type) ((type *)hypfs_alloc_dyndata(sizeof(type)))
 void *hypfs_get_dyndata(void);
 void hypfs_free_dyndata(void);
+int hypfs_read_dyndir_id_entry(const struct hypfs_entry_dir *template,
+                               unsigned int id, bool is_last,
+                               XEN_GUEST_HANDLE_PARAM(void) *uaddr);
+struct hypfs_entry *hypfs_gen_dyndir_id_entry(
+    const struct hypfs_entry_dir *template, unsigned int id, void *data);
+unsigned int hypfs_dynid_entry_size(const struct hypfs_entry *template,
+                                    unsigned int id);
 #endif
 
 #endif /* __XEN_HYPFS_H__ */
-- 
2.26.2