[PATCH] swsusp: struct snapshot_handle cleanup
Add comments describing struct snapshot_handle and its members, change the
confusing name of its member 'page' to 'cur'.
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Cc: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/kernel/power/power.h b/kernel/power/power.h
index 59ce712..1cefcf8 100644
--- a/kernel/power/power.h
+++ b/kernel/power/power.h
@@ -50,17 +50,65 @@
extern unsigned int count_data_pages(void);
+/**
+ * Auxiliary structure used for reading the snapshot image data and
+ * metadata from and writing them to the list of page backup entries
+ * (PBEs) which is the main data structure of swsusp.
+ *
+ * Using struct snapshot_handle we can transfer the image, including its
+ * metadata, as a continuous sequence of bytes with the help of
+ * snapshot_read_next() and snapshot_write_next().
+ *
+ * The code that writes the image to a storage or transfers it to
+ * the user land is required to use snapshot_read_next() for this
+ * purpose and it should not make any assumptions regarding the internal
+ * structure of the image. Similarly, the code that reads the image from
+ * a storage or transfers it from the user land is required to use
+ * snapshot_write_next().
+ *
+ * This may allow us to change the internal structure of the image
+ * in the future with considerably less effort.
+ */
+
struct snapshot_handle {
- loff_t offset;
- unsigned int page;
- unsigned int page_offset;
- unsigned int prev;
- struct pbe *pbe, *last_pbe;
- void *buffer;
- unsigned int buf_offset;
- int sync_read;
+ loff_t offset; /* number of the last byte ready for reading
+ * or writing in the sequence
+ */
+ unsigned int cur; /* number of the block of PAGE_SIZE bytes the
+ * next operation will refer to (ie. current)
+ */
+ unsigned int cur_offset; /* offset with respect to the current
+ * block (for the next operation)
+ */
+ unsigned int prev; /* number of the block of PAGE_SIZE bytes that
+ * was the current one previously
+ */
+ struct pbe *pbe; /* PBE that corresponds to 'buffer' */
+ struct pbe *last_pbe; /* When the image is restored (eg. read
+ * from disk) we can store some image
+ * data directly in the page frames
+ * in which they were before suspend.
+ * In such a case the PBEs that
+ * correspond to them will be unused.
+ * This is the last PBE, so far, that
+ * does not correspond to such data.
+ */
+ void *buffer; /* address of the block to read from
+ * or write to
+ */
+ unsigned int buf_offset; /* location to read from or write to,
+ * given as a displacement from 'buffer'
+ */
+ int sync_read; /* Set to one to notify the caller of
+ * snapshot_write_next() that it may
+ * need to call wait_on_bio_chain()
+ */
};
+/* This macro returns the address from/to which the caller of
+ * snapshot_read_next()/snapshot_write_next() is allowed to
+ * read/write data after the function returns
+ */
#define data_of(handle) ((handle).buffer + (handle).buf_offset)
extern int snapshot_read_next(struct snapshot_handle *handle, size_t count);