docs: deprecated.rst: Add note to the use of struct_size() helper
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PATCH v2 1/1 docs: deprecated.rst: Add note to the use of struct_size() helper
Add a note to educate people about the proper use of struct_size() when the trailing array in the enclosing structure is a one-element array.
Zero-length and one-element arrays will soon be removed from the kernel, but in the meantime, it's worth letting people know how to correctly use struct_size() together with such constructs.
Note: this documentation will be updated once all zero-length and one-element arrays have been completely removed from the kernel.
Signed-off-by Gustavo A. R. Silva <[email protected]>
---
Changes in v2:
- Suggest stop using one-element arrays and switch to flexible arrays.
- Update changelog text.
Documentation/process/deprecated.rst | 12 ++++++++++++ 1 file changed, 12 insertions(+)
Documentation/process/deprecated.rst +12 -0
@@ -85,6 +85,18 @@ Instead, use the helper:: header = kzalloc(struct_size(header, item, count), GFP_KERNEL); +NOTE: You might want to use the following form in case the trailing array +is a one-element array, as unlike zero-length arrays and flexible-array +members, `one-element arrays occupy at least as much space as a single +object of the type <https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html>`_, +hence they contribute to the size of the enclosing structure:: + + header = kzalloc(struct_size(header, item, count - 1), GFP_KERNEL); + +It's also worth noting that one-element arrays --together with zero-length +arrays-- will soon be completely removed from the codebase and deprecated. +So, you better STOP using them and switch to flexible arrays instead. + See array_size(), array3_size(), and struct_size(), for more details as well as the related check_add_overflow() and check_mul_overflow() family of functions.
Signature · 1 line
2.27.0