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Message-ID: <20071031084920.GA25202@havoc.gtf.org>
Date: Wed, 31 Oct 2007 04:49:20 -0400
From: Jeff Garzik <jeff@...zik.org>
To: Jens Axboe <jens.axboe@...cle.com>
Cc: linux-ide@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] "killing" sg_last(), and discussion
I looked into killing sg_last(), but really, this is the best its gonna
get (moving sg_last to libata-core.c).
You could maybe kill one use with caching, but in the other sg_last()
callsites there isn't another s/g loop we can stick a "last_sg = sg;"
into.
libata is stuck because we undertake the highly unusual operation of
fiddling with the final S/G element, to enforce 32-bit alignment.
Of course we could eliminate all that nasty fiddling/padding
completely, including sg_last(), if other areas of the kernel would
guarantee ahead of time that buffer lengths are always a multiple
of 4........
Jeff
[the obvious patch follows, moving sg_last()...]
drivers/ata/libata-core.c | 24 ++++++++++++++++++++++++
drivers/ata/sata_nv.c | 1 -
drivers/ata/sata_promise.c | 1 -
drivers/ata/sata_qstor.c | 1 -
include/linux/scatterlist.h | 34 ----------------------------------
5 files changed, 24 insertions(+), 37 deletions(-)
diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 63035d7..4f0acc5 100644
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -4480,6 +4480,30 @@ static unsigned int ata_dev_init_params(struct ata_device *dev,
}
/**
+ * sg_last - return the last scatterlist entry in a list
+ * @sgl: First entry in the scatterlist
+ * @nents: Number of entries in the scatterlist
+ *
+ * Description:
+ * Should only be used casually, it (currently) scan the entire list
+ * to get the last entry.
+ *
+ * Note that the @sgl@ pointer passed in need not be the first one,
+ * the important bit is that @nents@ denotes the number of entries that
+ * exist from @sgl@.
+ *
+ **/
+static inline struct scatterlist *sg_last(struct scatterlist *sgl,
+ unsigned int nents)
+{
+ struct scatterlist *sg, *ret = NULL;
+ unsigned int i;
+
+ for_each_sg(sgl, sg, nents, i)
+ ret = sg;
+}
+
+/**
* ata_sg_clean - Unmap DMA memory associated with command
* @qc: Command containing DMA memory to be released
*
diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
index 35b2df2..6546913 100644
--- a/drivers/ata/sata_nv.c
+++ b/drivers/ata/sata_nv.c
@@ -1985,7 +1985,6 @@ static void nv_swncq_fill_sg(struct ata_queued_cmd *qc)
struct nv_swncq_port_priv *pp = ap->private_data;
struct ata_prd *prd;
- WARN_ON(qc->__sg == NULL);
WARN_ON(qc->n_elem == 0 && qc->pad_len == 0);
prd = pp->prd + ATA_MAX_PRD * qc->tag;
diff --git a/drivers/ata/sata_promise.c b/drivers/ata/sata_promise.c
index 825e717..1fba9d4 100644
--- a/drivers/ata/sata_promise.c
+++ b/drivers/ata/sata_promise.c
@@ -547,7 +547,6 @@ static void pdc_fill_sg(struct ata_queued_cmd *qc)
if (!(qc->flags & ATA_QCFLAG_DMAMAP))
return;
- WARN_ON(qc->__sg == NULL);
WARN_ON(qc->n_elem == 0 && qc->pad_len == 0);
idx = 0;
diff --git a/drivers/ata/sata_qstor.c b/drivers/ata/sata_qstor.c
index 6d43ba7..664e3f7 100644
--- a/drivers/ata/sata_qstor.c
+++ b/drivers/ata/sata_qstor.c
@@ -276,7 +276,6 @@ static unsigned int qs_fill_sg(struct ata_queued_cmd *qc)
unsigned int nelem;
u8 *prd = pp->pkt + QS_CPB_BYTES;
- WARN_ON(qc->__sg == NULL);
WARN_ON(qc->n_elem == 0 && qc->pad_len == 0);
nelem = 0;
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 32326c2..ab94464 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -130,40 +130,6 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg)
for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))
/**
- * sg_last - return the last scatterlist entry in a list
- * @sgl: First entry in the scatterlist
- * @nents: Number of entries in the scatterlist
- *
- * Description:
- * Should only be used casually, it (currently) scan the entire list
- * to get the last entry.
- *
- * Note that the @sgl@ pointer passed in need not be the first one,
- * the important bit is that @nents@ denotes the number of entries that
- * exist from @sgl@.
- *
- **/
-static inline struct scatterlist *sg_last(struct scatterlist *sgl,
- unsigned int nents)
-{
-#ifndef ARCH_HAS_SG_CHAIN
- struct scatterlist *ret = &sgl[nents - 1];
-#else
- struct scatterlist *sg, *ret = NULL;
- unsigned int i;
-
- for_each_sg(sgl, sg, nents, i)
- ret = sg;
-
-#endif
-#ifdef CONFIG_DEBUG_SG
- BUG_ON(sgl[0].sg_magic != SG_MAGIC);
- BUG_ON(!sg_is_last(ret));
-#endif
- return ret;
-}
-
-/**
* sg_chain - Chain two sglists together
* @prv: First scatterlist
* @prv_nents: Number of entries in prv
-
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