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 stop comparing.
Signed-off-by: Douglas Gilbert <[email protected]> --- include/linux/scatterlist.h | 4 ++ lib/scatterlist.c | 84 ++++++++++++++++++++++++++++++++++++- 2 files changed, 86 insertions(+), 2 deletions(-) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 6649414c0749..ae260dc5fedb 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -325,6 +325,10 @@ 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); + /* * 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 1ec2c909c8d4..344725990b9d 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -979,10 +979,10 @@ 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 copying + * @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 copying + * @s_skip: Number of bytes to skip in source before starting * @n_bytes: The number of bytes to copy * * Returns the number of copied bytes. @@ -1060,3 +1060,83 @@ size_t sgl_copy_sgl(struct scatterlist *d_sgl, unsigned int d_nents, off_t d_ski } EXPORT_SYMBOL(sgl_copy_sgl); +/** + * 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 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. + * + * Same comment from sgl_copy_sgl() about large _skip arguments 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) +{ + bool equ = true; + size_t x_off, y_off, len, x_len, y_len; + size_t offset = 0; + struct sg_mapping_iter x_iter; + struct sg_mapping_iter y_iter; + + if (n_bytes == 0) + return true; + sg_miter_start(&x_iter, x_sgl, x_nents, SG_MITER_ATOMIC | SG_MITER_TO_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; + + for (x_off = 0, y_off = 0; true ; ) { + /* Assume x_iter.length and y_iter.length can never be 0 */ + if (x_off == 0) { + if (!sg_miter_next(&x_iter)) + break; + x_len = x_iter.length; + } else { + x_len = x_iter.length - x_off; + } + if (y_off == 0) { + if (!sg_miter_next(&y_iter)) + break; + y_len = y_iter.length; + } else { + y_len = y_iter.length - y_off; + } + len = min3(x_len, y_len, n_bytes - offset); + + equ = memcmp(x_iter.addr + x_off, y_iter.addr + y_off, len) == 0; + offset += len; + if (!equ || offset >= n_bytes) + break; + if (x_len == y_len) { + x_off = 0; + y_off = 0; + } else if (x_len < y_len) { + x_off = 0; + y_off += len; + } else { + x_off += len; + y_off = 0; + } + } +fini: + sg_miter_stop(&x_iter); + sg_miter_stop(&y_iter); + return equ; +} +EXPORT_SYMBOL(sgl_compare_sgl); -- 2.25.1
