Messages in this thread | | | Subject | Re: [PATCH v3 2/4] scatterlist: add sgl_copy_sgl() function | From | Bodo Stroesser <> | Date | Tue, 3 Nov 2020 14:26:10 +0100 |
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Am 19.10.20 um 21:19 schrieb Douglas Gilbert: > Both the SCSI and NVMe subsystems receive user data from the block > layer in scatterlist_s (aka scatter gather lists (sgl) which are > often arrays). If drivers in those subsystems represent storage > (e.g. a ramdisk) or cache "hot" user data then they may also > choose to use scatterlist_s. Currently there are no sgl to sgl > operations in the kernel. Start with a sgl to sgl copy. Stops > when the first of the number of requested bytes to copy, or the > source sgl, or the destination sgl is exhausted. So the > destination sgl will _not_ grow. > > Signed-off-by: Douglas Gilbert <dgilbert@interlog.com> > --- > include/linux/scatterlist.h | 4 ++ > lib/scatterlist.c | 75 +++++++++++++++++++++++++++++++++++++ > 2 files changed, 79 insertions(+) > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 80178afc2a4a..6649414c0749 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -321,6 +321,10 @@ size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents, > size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents, > size_t buflen, off_t skip); > > +size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_skip, > + struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip, > + size_t n_bytes); > + > /* > * Maximum number of entries that will be allocated in one piece, if > * a list larger than this is required then chaining will be utilized. > diff --git a/lib/scatterlist.c b/lib/scatterlist.c > index d5770e7f1030..1f9e093ad7da 100644 > --- a/lib/scatterlist.c > +++ b/lib/scatterlist.c > @@ -974,3 +974,78 @@ size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents, > return offset; > } > EXPORT_SYMBOL(sg_zero_buffer); > + > +/** > + * sgl_copy_sgl - Copy over a destination sgl from a source sgl > + * @d_sgl: Destination sgl > + * @d_nents: Number of SG entries in destination sgl > + * @d_skip: Number of bytes to skip in destination before starting > + * @s_sgl: Source sgl > + * @s_nents: Number of SG entries in source sgl > + * @s_skip: Number of bytes to skip in source before starting > + * @n_bytes: The (maximum) number of bytes to copy > + * > + * Returns: > + * The number of copied bytes. > + * > + * Notes: > + * Destination arguments appear before the source arguments, as with memcpy(). > + * > + * Stops copying if either d_sgl, s_sgl or n_bytes is exhausted. > + * > + * Since memcpy() is used, overlapping copies (where d_sgl and s_sgl belong > + * to the same sgl and the copy regions overlap) are not supported. > + * > + * Large copies are broken into copy segments whose sizes may vary. Those > + * copy segment sizes are chosen by the min3() statement in the code below. > + * Since SG_MITER_ATOMIC is used for both sides, each copy segment is started > + * with kmap_atomic() [in sg_miter_next()] and completed with kunmap_atomic() > + * [in sg_miter_stop()]. This means pre-emption is inhibited for relatively > + * short periods even in very large copies. > + * > + * If d_skip is large, potentially spanning multiple d_nents then some > + * integer arithmetic to adjust d_sgl may improve performance. For example > + * if d_sgl is built using sgl_alloc_order(chainable=false) then the sgl > + * will be an array with equally sized segments facilitating that > + * arithmetic. The suggestion applies to s_skip, s_sgl and s_nents as well. > + * > + **/ > +size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_skip, > + struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip, > + size_t n_bytes) > +{ > + size_t len; > + size_t offset = 0; > + struct sg_mapping_iter d_iter, s_iter; > + > + if (n_bytes == 0) > + return 0; > + sg_miter_start(&s_iter, s_sgl, s_nents, SG_MITER_ATOMIC | SG_MITER_FROM_SG); > + sg_miter_start(&d_iter, d_sgl, d_nents, SG_MITER_ATOMIC | SG_MITER_TO_SG); > + if (!sg_miter_skip(&s_iter, s_skip)) > + goto fini; > + if (!sg_miter_skip(&d_iter, d_skip)) > + goto fini; > + > + while (offset < n_bytes) { > + if (!sg_miter_next(&s_iter)) > + break; > + if (!sg_miter_next(&d_iter)) > + break; > + len = min3(d_iter.length, s_iter.length, n_bytes - offset); > + > + memcpy(d_iter.addr, s_iter.addr, len); > + offset += len; > + /* LIFO order (stop d_iter before s_iter) needed with SG_MITER_ATOMIC */ > + d_iter.consumed = len; > + sg_miter_stop(&d_iter); > + s_iter.consumed = len; > + sg_miter_stop(&s_iter); > + } > +fini: > + sg_miter_stop(&d_iter); > + sg_miter_stop(&s_iter); > + return offset; > +} > +EXPORT_SYMBOL(sgl_copy_sgl); > + >
Second try, this time with correct tag.
Reviewed-by: Bodo Stroesser <bostroesser@gmail.com>
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