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    SubjectRe: [PATCH v3 4/4] scatterlist: add sgl_memset()
    From
    Date
    Am 19.10.20 um 21:19 schrieb Douglas Gilbert:
    > The existing sg_zero_buffer() function is a bit restrictive.
    > For example protection information (PI) blocks are usually
    > initialized to 0xff bytes. As its name suggests sgl_memset()
    > is modelled on memset(). One difference is the type of the
    > val argument which is u8 rather than int. Plus it returns
    > the number of bytes (over)written.
    >
    > Change implementation of sg_zero_buffer() to call this new
    > function.
    >
    > Signed-off-by: Douglas Gilbert <dgilbert@interlog.com>
    > ---
    > include/linux/scatterlist.h | 3 ++
    > lib/scatterlist.c | 65 +++++++++++++++++++++++++------------
    > 2 files changed, 48 insertions(+), 20 deletions(-)
    >
    > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
    > index ae260dc5fedb..a40012c8a4e6 100644
    > --- a/include/linux/scatterlist.h
    > +++ b/include/linux/scatterlist.h
    > @@ -329,6 +329,9 @@ bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_sk
    > struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip,
    > size_t n_bytes);
    >
    > +size_t sgl_memset(struct scatterlist *sgl, unsigned int nents, off_t skip,
    > + u8 val, 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 49185536acba..6b430f7293e0 100644
    > --- a/lib/scatterlist.c
    > +++ b/lib/scatterlist.c
    > @@ -952,26 +952,7 @@ EXPORT_SYMBOL(sg_pcopy_to_buffer);
    > size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
    > size_t buflen, off_t skip)
    > {
    > - unsigned int offset = 0;
    > - struct sg_mapping_iter miter;
    > - unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;
    > -
    > - sg_miter_start(&miter, sgl, nents, sg_flags);
    > -
    > - if (!sg_miter_skip(&miter, skip))
    > - return false;
    > -
    > - while (offset < buflen && sg_miter_next(&miter)) {
    > - unsigned int len;
    > -
    > - len = min(miter.length, buflen - offset);
    > - memset(miter.addr, 0, len);
    > -
    > - offset += len;
    > - }
    > -
    > - sg_miter_stop(&miter);
    > - return offset;
    > + return sgl_memset(sgl, nents, skip, 0, buflen);
    > }
    > EXPORT_SYMBOL(sg_zero_buffer);
    >
    > @@ -1110,3 +1091,47 @@ bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_sk
    > return equ;
    > }
    > EXPORT_SYMBOL(sgl_compare_sgl);
    > +
    > +/**
    > + * sgl_memset - set byte 'val' up to n_bytes times on SG list
    > + * @sgl: The SG list
    > + * @nents: Number of SG entries in sgl
    > + * @skip: Number of bytes to skip before starting
    > + * @val: byte value to write to sgl
    > + * @n_bytes: The (maximum) number of bytes to modify
    > + *
    > + * Returns:
    > + * The number of bytes written.
    > + *
    > + * Notes:
    > + * Stops writing if either sgl or n_bytes is exhausted. If n_bytes is
    > + * set SIZE_MAX then val will be written to each byte until the end
    > + * of sgl.
    > + *
    > + * The notes in sgl_copy_sgl() about large sgl_s _applies here as well.
    > + *
    > + **/
    > +size_t sgl_memset(struct scatterlist *sgl, unsigned int nents, off_t skip,
    > + u8 val, size_t n_bytes)
    > +{
    > + size_t offset = 0;
    > + size_t len;
    > + struct sg_mapping_iter miter;
    > +
    > + if (n_bytes == 0)
    > + return 0;
    > + sg_miter_start(&miter, sgl, nents, SG_MITER_ATOMIC | SG_MITER_TO_SG);
    > + if (!sg_miter_skip(&miter, skip))
    > + goto fini;
    > +
    > + while ((offset < n_bytes) && sg_miter_next(&miter)) {
    > + len = min(miter.length, n_bytes - offset);
    > + memset(miter.addr, val, len);
    > + offset += len;
    > + }
    > +fini:
    > + sg_miter_stop(&miter);
    > + return offset;
    > +}
    > +EXPORT_SYMBOL(sgl_memset);
    > +
    >

    Reviewed-by: Bodo Stroesser <bostroesser@gmail.com>

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