Messages in this thread | | | Date | Tue, 11 Jan 2011 15:51:24 -0800 | From | Randy Dunlap <> | Subject | Re: [PATCH 1/4] scatterlist: new helper functions |
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On Wed, 12 Jan 2011 01:36:12 +0200 Maxim Levitsky wrote:
> 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. > > --- > include/linux/scatterlist.h | 6 ++ > lib/scatterlist.c | 137 +++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 143 insertions(+), 0 deletions(-)
> 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
kernel-doc notation for parameters is like so:
* @sg: the current sg entry
> + *
no empty line, please.
> + */ > +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
* @sg:
> + * > + * Allows to calculate dynamicly the lenght of the sg table, based on
dynamically the length
> + * 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
length
> + * @sg - the current sg entry
* @sg:
> + * > + * Dynamicly calculate total number of bytes in a sg list
Dynamically in an 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.
Add function parameters to kernel-doc, please.
> + */ > +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
pointed to by sg table
> + * to a kernel ram buffer
RAM
> + * @sg - the current sg entry > + * @buffer - linear buffer to compare with > + * @len - lenght of that buffer
* @sg: * @buffer: * @len: length
Returns 0 for equal or what??
> + */ > +bool sg_compare_to_buffer(struct scatterlist *sg, u8 *buffer, size_t len) > +{
Thanks for adding the kernel-doc.
--- ~Randy *** Remember to use Documentation/SubmitChecklist when testing your code ***
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