The question is with regard to the printk formats. The documentation that I’m reading is located here
Here is an excerpt that I’m asking about:
Physical addresses types phys_addr_t: %pa[p] 0x01234567 or 0x0123456789abcdef For printing a phys_addr_t type (and its derivatives, such as resource_size_t) which can vary based on build options, regardless of the width of the CPU data path. Passed by reference.
What does [p]
in %pa[p]
stand for? What does it mean?
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Answer
The p
in [p]
stands for phys_addr_t
when used in %pap
. This is analogous to the d
in %pad
stands for dma_addr_t
, as seen in the cited document:
DMA addresses types dma_addr_t: %pad 0x01234567 or 0x0123456789abcdef For printing a dma_addr_t type which can vary based on build options, regardless of the width of the CPU data path. Passed by reference.
Since it provides no documented difference between %pa
and %pap
, it means that they behave the same. The contents inside the brackets indicate optional modifiers. This is seen in the definition of %*pE
later in the document:
Raw buffer as an escaped string: %*pE[achnops] ... The conversion rules are applied according to an optional combination of flags (see string_escape_mem() kernel documentation for the details): a - ESCAPE_ANY c - ESCAPE_SPECIAL h - ESCAPE_HEX n - ESCAPE_NULL o - ESCAPE_OCTAL p - ESCAPE_NP s - ESCAPE_SPACE By default ESCAPE_ANY_NP is used.