[PATCH 1/4] Add envblk open functions to grub file interface

[Paul Dagnelie]

These functions are added to support the remainder of this patch set.
In order to add these special functions we have to refactor out the
logic that applies file filters so that it can be applied to both the
normal and envblk open functions.

commit 45ee383e11ecd15ac2820131d410a434eeea47a1
Author:     Paul Dagnelie <address@hidden>
AuthorDate: Mon Feb 24 11:19:40 2020 -0800
Commit:     Paul Dagnelie <address@hidden>
CommitDate: Tue Feb 25 10:08:07 2020 -0800

    Add support for special envblk functions in GRUB
---
 grub-core/kern/file.c | 76 +++++++++++++++++++++++++++++++++++++--------------
 include/grub/file.h   | 10 +++++++
 include/grub/fs.h     | 12 ++++++++
 3 files changed, 77 insertions(+), 21 deletions(-)

diff --git a/grub-core/kern/file.c b/grub-core/kern/file.c
index 58454458c..f929f61a0 100644
--- a/grub-core/kern/file.c
+++ b/grub-core/kern/file.c
@@ -57,14 +57,37 @@ grub_file_get_device_name (const char *name)
   return 0;
 }

+static grub_file_t
+grub_apply_file_filters (grub_file_t file, enum grub_file_type type,
const char *name)
+{
+  grub_file_filter_id_t filter;
+  grub_file_t last_file = NULL;
+
+  for (filter = 0; file && filter < ARRAY_SIZE (grub_file_filters);
+       filter++)
+    if (grub_file_filters[filter])
+      {
+    last_file = file;
+    file = grub_file_filters[filter] (file, type);
+    if (file && file != last_file)
+      {
+        file->name = grub_strdup (name);
+        grub_errno = GRUB_ERR_NONE;
+      }
+      }
+  if (!file)
+    grub_file_close (last_file);
+
+  return file;
+}
+
 grub_file_t
 grub_file_open (const char *name, enum grub_file_type type)
 {
-  grub_device_t device = 0;
-  grub_file_t file = 0, last_file = 0;
+  grub_device_t device = NULL;
+  grub_file_t file = NULL;
   char *device_name;
   const char *file_name;
-  grub_file_filter_id_t filter;

   device_name = grub_file_get_device_name (name);
   if (grub_errno)
@@ -113,22 +136,7 @@ grub_file_open (const char *name, enum grub_file_type type)
   file->name = grub_strdup (name);
   grub_errno = GRUB_ERR_NONE;

-  for (filter = 0; file && filter < ARRAY_SIZE (grub_file_filters);
-       filter++)
-    if (grub_file_filters[filter])
-      {
-    last_file = file;
-    file = grub_file_filters[filter] (file, type);
-    if (file && file != last_file)
-      {
-        file->name = grub_strdup (name);
-        grub_errno = GRUB_ERR_NONE;
-      }
-      }
-  if (!file)
-    grub_file_close (last_file);
-
-  return file;
+  return grub_apply_file_filters(file, type, name);

  fail:
   if (device)
@@ -141,6 +149,27 @@ grub_file_open (const char *name, enum grub_file_type type)
   return 0;
 }

+grub_file_t
+grub_file_envblk_open (grub_fs_t fs, grub_device_t device, enum
grub_file_type type)
+{
+  grub_file_t file = NULL;
+  file = (grub_file_t) grub_zalloc (sizeof (*file));
+  if (! file)
+    return NULL;
+  file->device = device;
+  file->envblk = 1;
+
+  if ((fs->fs_envblk_open) (file) != GRUB_ERR_NONE) {
+    grub_free(file);
+    return NULL;
+  }
+
+  file->fs = fs;
+  grub_errno = GRUB_ERR_NONE;
+
+  return grub_apply_file_filters(file, type, NULL);
+}
+
 grub_disk_read_hook_t grub_file_progress_hook;

 grub_ssize_t
@@ -177,7 +206,10 @@ grub_file_read (grub_file_t file, void *buf,
grub_size_t len)
       file->read_hook_data = file;
       file->progress_offset = file->offset;
     }
-  res = (file->fs->fs_read) (file, buf, len);
+  if (grub_file_envblk (file))
+    res = (file->fs->fs_envblk_read) (file, buf, len);
+  else
+    res = (file->fs->fs_read) (file, buf, len);
   file->read_hook = read_hook;
   file->read_hook_data = read_hook_data;
   if (res > 0)
@@ -189,7 +221,9 @@ grub_file_read (grub_file_t file, void *buf,
grub_size_t len)
 grub_err_t
 grub_file_close (grub_file_t file)
 {
-  if (file->fs->fs_close)
+  if (grub_file_envblk (file) && file->fs->fs_envblk_close)
+    (file->fs->fs_envblk_close) (file);
+  else if (file->fs->fs_close)
     (file->fs->fs_close) (file);

   if (file->device)
diff --git a/include/grub/file.h b/include/grub/file.h
index 31567483c..1cc688f55 100644
--- a/include/grub/file.h
+++ b/include/grub/file.h
@@ -170,6 +170,9 @@ struct grub_file

   /* Caller-specific data passed to the read hook.  */
   void *read_hook_data;
+
+  /* If the file is an FS's envblk, which uses separate functions for
interaction. */
+  int envblk;
 };
 typedef struct grub_file *grub_file_t;

@@ -211,6 +214,7 @@ grub_ssize_t EXPORT_FUNC(grub_file_read)
(grub_file_t file, void *buf,
                       grub_size_t len);
 grub_off_t EXPORT_FUNC(grub_file_seek) (grub_file_t file, grub_off_t offset);
 grub_err_t EXPORT_FUNC(grub_file_close) (grub_file_t file);
+grub_file_t EXPORT_FUNC(grub_file_envblk_open) (grub_fs_t fs,
grub_device_t device, enum grub_file_type type);

 /* Return value of grub_file_size() in case file size is unknown. */
 #define GRUB_FILE_SIZE_UNKNOWN     0xffffffffffffffffULL
@@ -233,6 +237,12 @@ grub_file_seekable (const grub_file_t file)
   return !file->not_easily_seekable;
 }

+static inline int
+grub_file_envblk (const grub_file_t file)
+{
+  return file->envblk;
+}
+
 grub_file_t
 grub_file_offset_open (grub_file_t parent, enum grub_file_type type,
                grub_off_t start, grub_off_t size);
diff --git a/include/grub/fs.h b/include/grub/fs.h
index 302e48d4b..ec1a7a50e 100644
--- a/include/grub/fs.h
+++ b/include/grub/fs.h
@@ -96,6 +96,18 @@ struct grub_fs
   /* Whether blocklist installs have a chance to work.  */
   int blocklist_install;
 #endif
+
+  /*
+   * The envblk functions are defined on filesystems that need to handle
+   * grub-writable files in a special way. This is most commonly the case for
+   * CoW filesystems like btrfs and ZFS.  The normal read and close functions
+   * should detect that they are being called on the envblk file and act
+   * appropriately.
+   */
+  grub_err_t (*fs_envblk_open) (struct grub_file *file);
+  grub_ssize_t (*fs_envblk_read) (struct grub_file *file, char *buf,
grub_size_t len);
+  grub_err_t (*fs_envblk_write) (struct grub_file *file, char *buf,
grub_size_t len);
+  grub_err_t (*fs_envblk_close) (struct grub_file *file);
 };
 typedef struct grub_fs *grub_fs_t;



--
Paul Dagnelie