To lay the foundation for a future change that converts MAP_PRIVATE-/dev/zero mappings to be truly anonymous, add the ability to uniquely identify these mappings.
With the memory character device now part of mm/ this is trivially achievable through a file_is_dev_zero() predicate that simply tests that the file operation hooks are zero_fops. Also update userland VMA tests to expose file_is_dev_zero() and provide a stub zero_fops for testing. Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]> --- mm/char-mem.c | 13 +++++++++++++ mm/internal.h | 3 +++ tools/testing/vma/include/dup.h | 7 +++++++ tools/testing/vma/shared.c | 9 +++++++++ 4 files changed, 32 insertions(+) diff --git a/mm/char-mem.c b/mm/char-mem.c index d2e575545044..e53e89e6ddd8 100644 --- a/mm/char-mem.c +++ b/mm/char-mem.c @@ -31,6 +31,8 @@ #include <linux/uaccess.h> #include <linux/security.h> +#include "internal.h" + #define DEVMEM_MINOR 1 #define DEVPORT_MINOR 4 @@ -707,6 +709,17 @@ static const struct memdev { #endif }; +/** + * file_is_dev_zero() - is the specified @file associated with the /dev/zero + * driver? + * @file: File to test. + * Returns: true if it is, false otherwise. + */ +bool file_is_dev_zero(const struct file *file) +{ + return file && file->f_op == &zero_fops; +} + static int memory_open(struct inode *inode, struct file *filp) { int minor; diff --git a/mm/internal.h b/mm/internal.h index e16f1250b25c..5d474e5f7709 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -1638,4 +1638,7 @@ static inline bool can_spin_trylock(void) return true; } +/* char-mem.c */ +bool file_is_dev_zero(const struct file *file); + #endif /* __MM_INTERNAL_H */ diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h index 57046d8ac81d..0d1a2ac88922 100644 --- a/tools/testing/vma/include/dup.h +++ b/tools/testing/vma/include/dup.h @@ -1641,3 +1641,10 @@ static inline pgoff_t linear_anon_page_index(const struct vm_area_struct *vma, return pgoff; } + +extern const struct file_operations zero_fops; + +static inline bool file_is_dev_zero(const struct file *file) +{ + return file && file->f_op == &zero_fops; +} diff --git a/tools/testing/vma/shared.c b/tools/testing/vma/shared.c index 4a39c9d50489..8c4826499f40 100644 --- a/tools/testing/vma/shared.c +++ b/tools/testing/vma/shared.c @@ -12,6 +12,15 @@ const struct vm_operations_struct vma_dummy_vm_ops; struct anon_vma dummy_anon_vma; struct task_struct __current; +static int mmap_zero_prepare(struct vm_area_desc *desc) +{ + return 0; +} + +const struct file_operations zero_fops = { + .mmap_prepare = mmap_zero_prepare, +}; + struct vm_area_struct *alloc_vma(struct mm_struct *mm, unsigned long start, unsigned long end, pgoff_t pgoff, vma_flags_t vma_flags) -- 2.55.0
