On 09.05.2023 10:28:13, Vincent MAILHOL wrote: > > > And because hdr.len is initially 3, hdr.len becomes 5. Right? Shouldn't it be 8? > > > > It might be a little confusing, but I think it's fine. > > hdr.len is given in units of longwords (4 bytes each)! Therefore we > > have 12 bytes (the initial 3 longwords) for struct tx_msg before > > tx_msg.data[]. > > Than (8 + 3)/4=2 gives us 2 additional longwords for the 8 data bytes. > > So that 3+2=5 (equal to 20 bytes) should be ok. I think the term longword is more commonly used in non-Unix operating systems :) > OK. So you want to round up the length to the next sizeof(long) multiple, right? > > First, sizeof(long) being platform specific, you need to declare a > macro to make your intent explicit. > > /* Size of a long int on esd devices */ > #define USB_ESD_SIZEOF_LONG 4 > > Please test, but for what I understand, below line is an equivalent > and a more readable way to achieve your goal: > > msg->hdr.len = DIV_ROUND_UP(cf->len, USB_ESD_SIZEOF_LONG); use "sizeof(u32)" > Also, add documentation to your structure to explain that hdr.len > represents the length in long, not in bytes. ...lengths in multiple of u32. Marc -- Pengutronix e.K. | Marc Kleine-Budde | Embedded Linux | https://www.pengutronix.de | Vertretung Nürnberg | Phone: +49-5121-206917-129 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-9 |
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