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Message-Id: <1294788975-19584-2-git-send-email-maximlevitsky@gmail.com>
Date: Wed, 12 Jan 2011 01:36:12 +0200
From: Maxim Levitsky <maximlevitsky@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Takashi Iwai <tiwai@...e.de>,
Alex Dubov <oakad@...oo.com>,
Maxim Levitsky <maximlevitsky@...il.com>
Subject: [PATCH 1/4] scatterlist: new helper functions
While developing memstick driver for legacy memsticks
I found the need in few helpers that I think should be
in common scatterlist library
The functions that were added:
* sg_nents/sg_total_len - iterate over scatterlist to figure
out total length of memory it covers / number of entries.
Useful for not keeping that information in side channels.
* sg_copy/sg_advance - Allow to break scatterlists apart into smaller chunks.
sg_copy creates smaller scatterlist, spanning first 'len' bytes, while
sg_advance edits the scatterlist in such way that it skips over 'len' bytes.
* sg_compare_to_buffer - another function to hide gory details of access
to sg list by CPU.
Allows to transparently compare contents of the sg list to given linear
buffer.
If needed later, a function that compares two sgs can be added.
All of this code is used by my ms_block.c driver.
Signed-off-by: Maxim Levitsky <maximlevitsky@...il.com>
---
include/linux/scatterlist.h | 6 ++
lib/scatterlist.c | 137 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 143 insertions(+), 0 deletions(-)
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 9aaf5bf..6305589 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -199,6 +199,11 @@ static inline void *sg_virt(struct scatterlist *sg)
return page_address(sg_page(sg)) + sg->offset;
}
+struct scatterlist *sg_advance(struct scatterlist *sg, int consumed);
+int sg_nents(struct scatterlist *sg);
+int sg_total_len(struct scatterlist *sg);
+int sg_copy(struct scatterlist *sg_from, struct scatterlist *sg_to, int len);
+
struct scatterlist *sg_next(struct scatterlist *);
struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
void sg_init_table(struct scatterlist *, unsigned int);
@@ -217,6 +222,7 @@ size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
void *buf, size_t buflen);
size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
void *buf, size_t buflen);
+bool sg_compare_to_buffer(struct scatterlist *sg, u8 *buffer, size_t len);
/*
* Maximum number of entries that will be allocated in one piece, if
diff --git a/lib/scatterlist.c b/lib/scatterlist.c
index 4ceb05d..2f18938 100644
--- a/lib/scatterlist.c
+++ b/lib/scatterlist.c
@@ -39,6 +39,77 @@ struct scatterlist *sg_next(struct scatterlist *sg)
EXPORT_SYMBOL(sg_next);
/**
+ * sg_advance - advance scatterlist by 'consumed' bytes
+ * @sg - the current sg entry
+ * @consumed - how much bytes to advance
+ *
+ */
+struct scatterlist *sg_advance(struct scatterlist *sg, int consumed)
+{
+ while (consumed >= sg->length) {
+ consumed -= sg->length;
+
+ sg = sg_next(sg);
+ if (!sg)
+ break;
+ }
+
+ WARN_ON(!sg && consumed);
+
+ if (!sg)
+ return NULL;
+
+ sg->offset += consumed;
+ sg->length -= consumed;
+
+ if (sg->offset >= PAGE_SIZE) {
+ struct page *page =
+ nth_page(sg_page(sg), sg->offset / PAGE_SIZE);
+ sg_set_page(sg, page, sg->length, sg->offset % PAGE_SIZE);
+ }
+
+ return sg;
+}
+EXPORT_SYMBOL(sg_advance);
+
+/**
+ * sg_nents - calculate number of sg entries in sg list
+ * @sg - the current sg entry
+ *
+ * Allows to calculate dynamicly the lenght of the sg table, based on
+ * assumption that last entry is NULL
+ */
+int sg_nents(struct scatterlist *sg)
+{
+ int nents = 0;
+ while (sg) {
+ nents++;
+ sg = sg_next(sg);
+ }
+
+ return nents;
+}
+EXPORT_SYMBOL(sg_nents);
+
+/**
+ * sg_total_len - calculate total lenght of scatterlist
+ * @sg - the current sg entry
+ *
+ * Dynamicly calculate total number of bytes in a sg list
+ * based on assumption that list ends with a NULL entry
+ */
+int sg_total_len(struct scatterlist *sg)
+{
+ int len = 0;
+ while (sg) {
+ len += sg->length;
+ sg = sg_next(sg);
+ }
+ return len;
+}
+EXPORT_SYMBOL(sg_total_len);
+
+/**
* sg_last - return the last scatterlist entry in a list
* @sgl: First entry in the scatterlist
* @nents: Number of entries in the scatterlist
@@ -110,6 +181,33 @@ void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
}
EXPORT_SYMBOL(sg_init_one);
+/**
+ * sg_copy - copies sg entries from sg_from to sg_to, such
+ * as sg_to covers first 'len' bytes from sg_from.
+ */
+int sg_copy(struct scatterlist *sg_from, struct scatterlist *sg_to, int len)
+{
+ while (len > sg_from->length) {
+ len -= sg_from->length;
+
+ sg_set_page(sg_to, sg_page(sg_from),
+ sg_from->length, sg_from->offset);
+
+ sg_to = sg_next(sg_to);
+ sg_from = sg_next(sg_from);
+
+ if (len && (!sg_from || !sg_to))
+ return -ENOMEM;
+ }
+
+ if (len)
+ sg_set_page(sg_to, sg_page(sg_from),
+ len, sg_from->offset);
+ sg_mark_end(sg_to);
+ return 0;
+}
+EXPORT_SYMBOL(sg_copy);
+
/*
* The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
* helpers.
@@ -517,3 +615,42 @@ size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
return sg_copy_buffer(sgl, nents, buf, buflen, 1);
}
EXPORT_SYMBOL(sg_copy_to_buffer);
+
+
+/**
+ * sg_compare_to_buffer - compare contents of the data pointeted by sg table
+ * to a kernel ram buffer
+ * @sg - the current sg entry
+ * @buffer - linear buffer to compare with
+ * @len - lenght of that buffer
+ */
+bool sg_compare_to_buffer(struct scatterlist *sg, u8 *buffer, size_t len)
+{
+ unsigned long flags;
+ int retval = 0;
+ struct sg_mapping_iter miter;
+
+ if (sg_total_len(sg) < len)
+ return 1;
+
+ local_irq_save(flags);
+ sg_miter_start(&miter, sg, sg_nents(sg),
+ SG_MITER_ATOMIC | SG_MITER_FROM_SG);
+
+ while (sg_miter_next(&miter) && len > 0) {
+
+ int cmplen = min(miter.length, len);
+ if (memcmp(miter.addr, buffer, cmplen)) {
+ retval = 1;
+ break;
+ }
+
+ buffer += cmplen;
+ len -= cmplen;
+ }
+
+ sg_miter_stop(&miter);
+ local_irq_restore(flags);
+ return retval;
+}
+EXPORT_SYMBOL(sg_compare_to_buffer);
--
1.7.1
--
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