| Message ID | 20210118163006.61659-4-dgilbert@interlog.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | scatterlist: add new capabilities | expand |
On Mon, 18 Jan 2021 11:30:05 -0500, Douglas Gilbert wrote: > After enabling copies between scatter gather lists (sgl_s), another > storage related operation is to compare two sgl_s. This new function > is modelled on NVMe's Compare command and the SCSI VERIFY(BYTCHK=1) > command. Like memcmp() this function returns false on the first > miscompare and stops comparing. > > A helper function called sgl_compare_sgl_idx() is added. It takes an > additional parameter (miscompare_idx) which is a pointer. If that > pointer is non-NULL and a miscompare is detected (i.e. the function > returns false) then the byte index of the first miscompare is written > to *miscomapre_idx. Knowing the location of the first miscompare is > needed to implement the SCSI COMPARE AND WRITE command properly. > > Reviewed-by: Bodo Stroesser <bostroesser@gmail.com> > Signed-off-by: Douglas Gilbert <dgilbert@interlog.com> > --- > include/linux/scatterlist.h | 8 +++ > lib/scatterlist.c | 109 ++++++++++++++++++++++++++++++++++++ > 2 files changed, 117 insertions(+) > > diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h > index 3f836a3246aa..71be65f9ebb5 100644 > --- a/include/linux/scatterlist.h > +++ b/include/linux/scatterlist.h > @@ -325,6 +325,14 @@ size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_ski > struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip, > size_t n_bytes); > > +bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, > + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, > + size_t n_bytes); > + > +bool sgl_compare_sgl_idx(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, > + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, > + size_t n_bytes, size_t *miscompare_idx); This patch looks good and works fine as a replacement for compare_and_write_do_cmp(). One minor suggestion would be to name it sgl_equal() or similar, to perhaps better reflect the bool return and avoid memcmp() confusion. Either way: Reviewed-by: David Disseldorp <ddiss@suse.de> Cheers, David
On 2021-01-18 6:27 p.m., David Disseldorp wrote: > On Mon, 18 Jan 2021 11:30:05 -0500, Douglas Gilbert wrote: > >> After enabling copies between scatter gather lists (sgl_s), another >> storage related operation is to compare two sgl_s. This new function >> is modelled on NVMe's Compare command and the SCSI VERIFY(BYTCHK=1) >> command. Like memcmp() this function returns false on the first >> miscompare and stops comparing. >> >> A helper function called sgl_compare_sgl_idx() is added. It takes an >> additional parameter (miscompare_idx) which is a pointer. If that >> pointer is non-NULL and a miscompare is detected (i.e. the function >> returns false) then the byte index of the first miscompare is written >> to *miscomapre_idx. Knowing the location of the first miscompare is >> needed to implement the SCSI COMPARE AND WRITE command properly. >> >> Reviewed-by: Bodo Stroesser <bostroesser@gmail.com> >> Signed-off-by: Douglas Gilbert <dgilbert@interlog.com> >> --- >> include/linux/scatterlist.h | 8 +++ >> lib/scatterlist.c | 109 ++++++++++++++++++++++++++++++++++++ >> 2 files changed, 117 insertions(+) >> >> diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h >> index 3f836a3246aa..71be65f9ebb5 100644 >> --- a/include/linux/scatterlist.h >> +++ b/include/linux/scatterlist.h >> @@ -325,6 +325,14 @@ size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_ski >> struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip, >> size_t n_bytes); >> >> +bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, >> + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, >> + size_t n_bytes); >> + >> +bool sgl_compare_sgl_idx(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, >> + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, >> + size_t n_bytes, size_t *miscompare_idx); > > > This patch looks good and works fine as a replacement for > compare_and_write_do_cmp(). One minor suggestion would be to name it > sgl_equal() or similar, to perhaps better reflect the bool return and > avoid memcmp() confusion. Either way: > Reviewed-by: David Disseldorp <ddiss@suse.de> Thanks. NVMe calls the command that does this Compare and SCSI uses COMPARE AND WRITE (and VERIFY(BYTCHK=1) ) but "equal" is fine with me. There will be another patchset version (at least) so there is time to change. Do you want: - sgl_equal(...), or - sgl_equal_sgl(...) ? Doug Gilbert
On Mon, 18 Jan 2021 20:04:20 -0500, Douglas Gilbert wrote: > >> +bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, > >> + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, > >> + size_t n_bytes); > >> + > >> +bool sgl_compare_sgl_idx(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, > >> + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, > >> + size_t n_bytes, size_t *miscompare_idx); > > > > > > This patch looks good and works fine as a replacement for > > compare_and_write_do_cmp(). One minor suggestion would be to name it > > sgl_equal() or similar, to perhaps better reflect the bool return and > > avoid memcmp() confusion. Either way: > > Reviewed-by: David Disseldorp <ddiss@suse.de> > > Thanks. NVMe calls the command that does this Compare and SCSI uses > COMPARE AND WRITE (and VERIFY(BYTCHK=1) ) but "equal" is fine with me. > There will be another patchset version (at least) so there is time > to change. > > Do you want: > - sgl_equal(...), or > - sgl_equal_sgl(...) ? I'd probably prefer the former as it's shorter, but I don't feel strongly about it. The latter would make sense if you expect sgl compare helpers for other buffer types. Cheers, David
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 3f836a3246aa..71be65f9ebb5 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -325,6 +325,14 @@ size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_ski struct scatterlist *s_sgl, unsigned int s_nents, off_t s_skip, size_t n_bytes); +bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, + size_t n_bytes); + +bool sgl_compare_sgl_idx(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, + size_t n_bytes, size_t *miscompare_idx); + /* * 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 c06f8caaff91..e3182de753d0 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -1131,3 +1131,112 @@ size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_ski return offset; } EXPORT_SYMBOL(sgl_copy_sgl); + +/** + * sgl_compare_sgl_idx - Compare x and y (both sgl_s) + * @x_sgl: x (left) sgl + * @x_nents: Number of SG entries in x (left) sgl + * @x_skip: Number of bytes to skip in x (left) before starting + * @y_sgl: y (right) sgl + * @y_nents: Number of SG entries in y (right) sgl + * @y_skip: Number of bytes to skip in y (right) before starting + * @n_bytes: The (maximum) number of bytes to compare + * @miscompare_idx: if return is false, index of first miscompare written + * to this pointer (if non-NULL). Value will be < n_bytes + * + * 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). If return + * is false and miscompare_idx is non-NULL, then index of first miscompared + * byte written to *miscompare_idx. + * + * Notes: + * x and y are symmetrical: they can be swapped and the result is the same. + * + * Implementation is based on memcmp(). x and y segments may overlap. + * + * The notes in sgl_copy_sgl() about large sgl_s _applies here as well. + * + **/ +bool sgl_compare_sgl_idx(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, + size_t n_bytes, size_t *miscompare_idx) +{ + bool equ = true; + size_t len; + size_t offset = 0; + struct sg_mapping_iter x_iter, y_iter; + + if (n_bytes == 0) + return true; + sg_miter_start(&x_iter, x_sgl, x_nents, SG_MITER_ATOMIC | SG_MITER_FROM_SG); + sg_miter_start(&y_iter, y_sgl, y_nents, SG_MITER_ATOMIC | SG_MITER_FROM_SG); + if (!sg_miter_skip(&x_iter, x_skip)) + goto fini; + if (!sg_miter_skip(&y_iter, y_skip)) + goto fini; + + while (offset < n_bytes) { + if (!sg_miter_next(&x_iter)) + break; + if (!sg_miter_next(&y_iter)) + break; + len = min3(x_iter.length, y_iter.length, n_bytes - offset); + + equ = !memcmp(x_iter.addr, y_iter.addr, len); + if (!equ) + goto fini; + offset += len; + /* LIFO order is important when SG_MITER_ATOMIC is used */ + y_iter.consumed = len; + sg_miter_stop(&y_iter); + x_iter.consumed = len; + sg_miter_stop(&x_iter); + } +fini: + if (miscompare_idx && !equ) { + u8 *xp = x_iter.addr; + u8 *yp = y_iter.addr; + u8 *x_endp; + + for (x_endp = xp + len ; xp < x_endp; ++xp, ++yp) { + if (*xp != *yp) + break; + } + *miscompare_idx = offset + len - (x_endp - xp); + } + sg_miter_stop(&y_iter); + sg_miter_stop(&x_iter); + return equ; +} +EXPORT_SYMBOL(sgl_compare_sgl_idx); + +/** + * sgl_compare_sgl - Compare x and y (both sgl_s) + * @x_sgl: x (left) sgl + * @x_nents: Number of SG entries in x (left) sgl + * @x_skip: Number of bytes to skip in x (left) before starting + * @y_sgl: y (right) sgl + * @y_nents: Number of SG entries in y (right) 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). + * + * Notes: + * x and y are symmetrical: they can be swapped and the result is the same. + * + * Implementation is based on memcmp(). x and y segments may overlap. + * + * The notes in sgl_copy_sgl() about large sgl_s _applies here as well. + * + **/ +bool sgl_compare_sgl(struct scatterlist *x_sgl, unsigned int x_nents, off_t x_skip, + struct scatterlist *y_sgl, unsigned int y_nents, off_t y_skip, + size_t n_bytes) +{ + return sgl_compare_sgl_idx(x_sgl, x_nents, x_skip, y_sgl, y_nents, y_skip, n_bytes, NULL); +} +EXPORT_SYMBOL(sgl_compare_sgl);