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The scatterwalk_* functions are designed to advance to the next sg entry only when there is more data from the request to process. Compared to the alternative of advancing after each step if !sg_is_last(sg), this has the advantage that it doesn't cause problems if users accidentally don't terminate their scatterlist with the end marker (which is an easy mistake to make, and there are examples of this). Currently, the advance to the next sg entry happens in scatterwalk_done(), which is called after each "step" of the walk. It requires the caller to pass in a boolean 'more' that indicates whether there is more data. This works when the caller immediately knows whether there is more data, though it adds some complexity. However in the case of scatterwalk_copychunks() it's not immediately known whether there is more data, so the call to scatterwalk_done() has to happen higher up the stack. This is error-prone, and indeed the needed call to scatterwalk_done() is not always made, e.g. scatterwalk_copychunks() is sometimes called multiple times in a row. This causes a zero-length step to get added in some cases, which is unexpected and seems to work only by accident. This patch begins the switch to a less error-prone approach where the advance to the next sg entry happens just in time instead. For now, that means just doing the advance in scatterwalk_clamp() if it's needed there. Initially this is redundant, but it's needed to keep the tree in a working state as later patches change things to the final state. Later patches will similarly move the dcache flushing logic out of scatterwalk_done() and then remove scatterwalk_done() entirely. Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.