There is pre-existing logic that appears to be undocumented for an mremap() shrink operation, where it turns out that the usual 'input range must span a single mapping' requirement no longer applies. In fact, it turns out that the input range specified by [old_address, old_address + old_size) may span any number of mappings. If shrinking in-place (that is, neither the MREMAP_FIXED nor MREMAP_DONTUNMAP flags are specified), then the new span may also span any number of VMAs - [old_address, old_address + new_size). If shrinking and moving, the range specified by [old_address, old_address + new_size) must span a single VMA. There must be at least one VMA contained within the [old_address, old_address + old_size) range, and old_address must be within the range of a VMA. Explicitly document this. Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx> --- man/man2/mremap.2 | 31 +++++++++++++++++++++++++++++-- 1 file changed, 29 insertions(+), 2 deletions(-) diff --git a/man/man2/mremap.2 b/man/man2/mremap.2 index 6ba51310c..631c835b8 100644 --- a/man/man2/mremap.2 +++ b/man/man2/mremap.2 @@ -48,8 +48,35 @@ The .B MREMAP_DONTUNMAP flag may be specified. .P -If the operation is not -simply moving mappings, +Equally, if the operation performs a shrink, +that is if +.I old_size +is greater than +.IR new_size , +then +.I old_size +may also span multiple mappings +which do not have to be +adjacent to one another. +If this shrink is performed +in-place, +that is, +neither +.BR MREMAP_FIXED , +nor +.B MREMAP_DONTUNMAP +are specified, +.I new_size +may also span multiple VMAs. +However, if the range is moved, +then +.I new_size +must span only a single mapping. +.P +If the operation is neither a +.B MREMAP_FIXED +move +nor a shrink, then .I old_size must span only a single mapping. -- 2.50.1
