[PATCH v3 6/8] verifiers: Add the documentation

[Daniel Kiper <daniel.kiper@oracle.com>]

From: Vladimir Serbinenko <phcoder@gmail.com>

Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
---
v3 - suggestions/fixes:
   - improve the documentation.
---
 docs/grub-dev.texi |   57 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/docs/grub-dev.texi b/docs/grub-dev.texi
index a9f4de6..ad72705 100644
--- a/docs/grub-dev.texi
+++ b/docs/grub-dev.texi
@@ -84,6 +84,7 @@ This edition documents version @value{VERSION}.
 * Video Subsystem::
 * PFF2 Font File Format::
 * Graphical Menu Software Design::
+* Verifiers framework::
 * Copying This Manual::         Copying This Manual
 * Index::
 @end menu
@@ -1949,6 +1950,62 @@ the graphics mode that was in use before @code{grub_video_setup()} was called
 might fix some of the problems.
 
 
+@node Verifiers framework
+@chapter Verifiers framework
+
+To register your own verifier call @samp{grub_verifier_register} with a
+structure pointing to your functions.
+
+The interface is inspired by hash interface with @samp{init}/@samp{write}/@samp{fini}.
+
+There are eesntially 2 ways of using it: hashing and whole-file verification:
+
+With hashing approach:
+During @samp{init} you decide whether you want to check given file and init context.
+In @samp{write} you update you hashing state.
+In @samp{fini} you check that hash matches the expected value/passes some check/...
+
+With whole-file verification:
+During @samp{init} you decide whether you want to check given file and init context.
+In @samp{write} you verify file and return error if it fails.
+You don't have @samp{fini}.
+
+Additional @samp{verify_string} receives various strings like kernel parameters to
+verify. Returning no error means successful verification and an error stops the current
+action.
+
+Detailed description of API:
+
+Every time a file is opened your @samp{init} function is called with file descriptor
+and file type. Your function can have following outcomes:
+
+@itemize
+
+@item returning no error and setting @samp{*flags} to @samp{GRUB_VERIFY_FLAGS_DEFER}.
+In this case verification is deferred to others active verifiers. Verification fails if
+nobody cares or selected verifier fails
+
+@item returning no error and setting @samp{*flags} to @samp{GRUB_VERIFY_FLAGS_SKIP_VERIFICATION}.
+In this case your verifier will not be called anymore and your verifier is considered
+to have skipped verification
+
+@item returning error. Then opening of the file will fail due to failed verification.
+
+@item returning no error and not setting @samp{*flags} to @samp{GRUB_VERIFY_FLAGS_SKIP_VERIFICATION}
+In this case verification is done as described in following section
+
+@end itemize
+
+In the fourth case your @samp{write} will be called with chunks of file. If you need the whole file in a single
+chunk then during @samp{init} set bit @samp{GRUB_VERIFY_FLAGS_SINGLE_CHUNK} in @samp{*flags}.
+During @samp{init} you may set @samp{*context} if you need additional context. At every iteration you may return
+an error and the the file will be considered as having failed the verification. If you return no error then
+verification continues.
+
+Optionally at the end of the file @samp{fini} if it exists is called with just the context. If you return
+no error during any of @samp{init}, @samp{write} and @samp{fini} then the file is considered as having
+succeded verification.
+
 @node Copying This Manual
 @appendix Copying This Manual
 
-- 
1.7.10.4