| Message ID | 20201018171336.63839-5-dgilbert@interlog.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | scatterlist: add new capabilities | expand |
AFAICS, there are 2 unneeded lines in the new implementation of sgl_memset. Please see details below. Am 18.10.20 um 19:13 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. > > Signed-off-by: Douglas Gilbert <dgilbert@interlog.com> > --- ... > + > +/** > + * 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; > + miter.consumed = len; The above line will not change miter.consumed in all loop cycles but the last, since len will be miter.length for all loop cycles but the last and sg_miter_next initializes miter.consumed to contain miter.length. In the last loop cycle it does not harm if miter.consumed stays bigger than len. So this line is not needed and can be removed. > + sg_miter_stop(&miter); Since the code does not use nested sg_miter, the sg_miter_stop() here is not needed, you can remove that line. Either the next call to sg_miter_next will call sg_miter_stop before preparing next chunk of mem, or sg_miter_stop is called behind the loop. > + } > +fini: > + sg_miter_stop(&miter); > + return offset; > +} > +EXPORT_SYMBOL(sgl_memset); > + >
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 d910776a4c96..a704039ab54d 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -985,7 +985,8 @@ EXPORT_SYMBOL(sg_zero_buffer); * @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. + * Returns: + * The number of copied bytes. * * Notes: * Destination arguments appear before the source arguments, as with memcpy(). @@ -1058,8 +1059,9 @@ EXPORT_SYMBOL(sgl_copy_sgl); * @y_skip: Number of bytes to skip in y (right) before starting * @n_bytes: The (maximum) number of bytes to compare * - * Returns true if x and y compare equal before x, y or n_bytes is exhausted. - * Otherwise on a miscompare, returns false (and stops comparing). + * Returns: + * true if x and y compare equal before x, y or n_bytes is exhausted. + * Otherwise on a miscompare, returns false (and stops comparing). * * Notes: * x and y are symmetrical: they can be swapped and the result is the same. @@ -1108,3 +1110,49 @@ 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; + miter.consumed = len; + sg_miter_stop(&miter); + } +fini: + sg_miter_stop(&miter); + return offset; +} +EXPORT_SYMBOL(sgl_memset); +
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. Signed-off-by: Douglas Gilbert <dgilbert@interlog.com> --- include/linux/scatterlist.h | 3 +++ lib/scatterlist.c | 54 ++++++++++++++++++++++++++++++++++--- 2 files changed, 54 insertions(+), 3 deletions(-)