write.2: explain the atomicity guarantees of the writes

[kib]

Summary

Also provide the pointer to the latest POSIX standard that justifies the
requirement.

[rmacklem]

lib/libsys/write.2

139

As required.. doesn't sound quite right to me?
Maybe "This is required by the POSIX standard"

(But, I won't claim to be a decent writer, so I'll
let you decide if it needs changing.)

151

"i" -> "I"

[emaste]

lib/libsys/write.2

137–138

I would write "effects of write" (although "write effects" is also understandable)

139

I think this is OK but the example inline makes it a bit awkward as it's a long sentence.

Could be split into two sentences if desired, something like:

As required by the POSIX standard, the read, write and ftruncate functions and their variations...
See .St -p1003.1-2024 ... for more information.

151

The .Fx above is FreeBSD, so FreeBSD implements the ...

My take on this sentence would be:

FreeBSD implementes the requirement by taking a read/write range lock on the file byte range affected by the corresponding function.

[rmacklem]

Oh, and it needs the date to be updated.

[kib]

Edit according to reviewer's suggestions.