[PATCH] swsusp: struct snapshot_handle cleanup
Rafael J. Wysocki [Tue, 26 Sep 2006 06:32:46 +0000 (23:32 -0700)]
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>

kernel/power/power.h
kernel/power/snapshot.c

index 59ce712..1cefcf8 100644 (file)
@@ -50,17 +50,65 @@ extern asmlinkage int swsusp_arch_resume(void);
 
 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);
index 979096c..81fe8de 100644 (file)
@@ -555,7 +555,7 @@ static inline struct pbe *pack_orig_addresses(unsigned long *buf, struct pbe *pb
 
 int snapshot_read_next(struct snapshot_handle *handle, size_t count)
 {
-       if (handle->page > nr_meta_pages + nr_copy_pages)
+       if (handle->cur > nr_meta_pages + nr_copy_pages)
                return 0;
        if (!buffer) {
                /* This makes the buffer be freed by swsusp_free() */
@@ -568,8 +568,8 @@ int snapshot_read_next(struct snapshot_handle *handle, size_t count)
                handle->buffer = buffer;
                handle->pbe = pagedir_nosave;
        }
-       if (handle->prev < handle->page) {
-               if (handle->page <= nr_meta_pages) {
+       if (handle->prev < handle->cur) {
+               if (handle->cur <= nr_meta_pages) {
                        handle->pbe = pack_orig_addresses(buffer, handle->pbe);
                        if (!handle->pbe)
                                handle->pbe = pagedir_nosave;
@@ -577,15 +577,15 @@ int snapshot_read_next(struct snapshot_handle *handle, size_t count)
                        handle->buffer = (void *)handle->pbe->address;
                        handle->pbe = handle->pbe->next;
                }
-               handle->prev = handle->page;
+               handle->prev = handle->cur;
        }
-       handle->buf_offset = handle->page_offset;
-       if (handle->page_offset + count >= PAGE_SIZE) {
-               count = PAGE_SIZE - handle->page_offset;
-               handle->page_offset = 0;
-               handle->page++;
+       handle->buf_offset = handle->cur_offset;
+       if (handle->cur_offset + count >= PAGE_SIZE) {
+               count = PAGE_SIZE - handle->cur_offset;
+               handle->cur_offset = 0;
+               handle->cur++;
        } else {
-               handle->page_offset += count;
+               handle->cur_offset += count;
        }
        handle->offset += count;
        return count;
@@ -820,7 +820,7 @@ int snapshot_write_next(struct snapshot_handle *handle, size_t count)
 {
        int error = 0;
 
-       if (handle->prev && handle->page > nr_meta_pages + nr_copy_pages)
+       if (handle->prev && handle->cur > nr_meta_pages + nr_copy_pages)
                return 0;
        if (!buffer) {
                /* This makes the buffer be freed by swsusp_free() */
@@ -831,7 +831,7 @@ int snapshot_write_next(struct snapshot_handle *handle, size_t count)
        if (!handle->offset)
                handle->buffer = buffer;
        handle->sync_read = 1;
-       if (handle->prev < handle->page) {
+       if (handle->prev < handle->cur) {
                if (!handle->prev) {
                        error = load_header(handle,
                                        (struct swsusp_info *)buffer);
@@ -854,15 +854,15 @@ int snapshot_write_next(struct snapshot_handle *handle, size_t count)
                        handle->buffer = get_buffer(handle);
                        handle->sync_read = 0;
                }
-               handle->prev = handle->page;
+               handle->prev = handle->cur;
        }
-       handle->buf_offset = handle->page_offset;
-       if (handle->page_offset + count >= PAGE_SIZE) {
-               count = PAGE_SIZE - handle->page_offset;
-               handle->page_offset = 0;
-               handle->page++;
+       handle->buf_offset = handle->cur_offset;
+       if (handle->cur_offset + count >= PAGE_SIZE) {
+               count = PAGE_SIZE - handle->cur_offset;
+               handle->cur_offset = 0;
+               handle->cur++;
        } else {
-               handle->page_offset += count;
+               handle->cur_offset += count;
        }
        handle->offset += count;
        return count;
@@ -871,5 +871,5 @@ int snapshot_write_next(struct snapshot_handle *handle, size_t count)
 int snapshot_image_loaded(struct snapshot_handle *handle)
 {
        return !(!handle->pbe || handle->pbe->next || !nr_copy_pages ||
-               handle->page <= nr_meta_pages + nr_copy_pages);
+               handle->cur <= nr_meta_pages + nr_copy_pages);
 }