From 00cdf76012ab78b225345e8cf77d5391b4680b45 Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Thu, 26 Jan 2023 20:15:52 +0000 Subject: mm: add memcpy_from_file_folio() This is the equivalent of memcpy_from_page(). It differs in that it takes the position in a file instead of offset in a folio, it accepts the total number of bytes to be copied (instead of the number of bytes to be copied from this folio) and it returns how many bytes were copied from the folio, rather than making the caller calculate that and then checking if the caller got it right. [akpm@linux-foundation.org: fix typo in comment] Link: https://lkml.kernel.org/r/20230126201552.1681588-1-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Cc: "Fabio M. De Francesco" Cc: Ira Weiny Signed-off-by: Andrew Morton --- include/linux/highmem.h | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) (limited to 'include/linux/highmem.h') diff --git a/include/linux/highmem.h b/include/linux/highmem.h index e22509420ac6..348701dae77f 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -413,6 +413,35 @@ static inline void memzero_page(struct page *page, size_t offset, size_t len) kunmap_local(addr); } +/** + * memcpy_from_file_folio - Copy some bytes from a file folio. + * @to: The destination buffer. + * @folio: The folio to copy from. + * @pos: The position in the file. + * @len: The maximum number of bytes to copy. + * + * Copy up to @len bytes from this folio. This may be limited by PAGE_SIZE + * if the folio comes from HIGHMEM, and by the size of the folio. + * + * Return: The number of bytes copied from the folio. + */ +static inline size_t memcpy_from_file_folio(char *to, struct folio *folio, + loff_t pos, size_t len) +{ + size_t offset = offset_in_folio(folio, pos); + char *from = kmap_local_folio(folio, offset); + + if (folio_test_highmem(folio)) + len = min_t(size_t, len, PAGE_SIZE - offset); + else + len = min(len, folio_size(folio) - offset); + + memcpy(to, from, len); + kunmap_local(from); + + return len; +} + /** * folio_zero_segments() - Zero two byte ranges in a folio. * @folio: The folio to write to. -- cgit v1.2.3