CODEWITHSUNDEEP
unix
Daneill
Daneill

Reputation: 23

how does msync() work?

I use mmap to map file F to block B, and then I only write one byte of B. If I call msync() for B with MS_SYNC, does the OS write all the block to F? Or it only writes the one byte modified to F?

Upvotes: 0

Views: 652

Answers (2)

Randy Howard
Randy Howard

Reputation: 2156

What does the man page on your particular system say? If it's not open source, that's about the best you have to go on, unless you have can find more detailed documentation for your UNIX platform.

On at least one system, man msync says:

The msync() system call writes modified whole pages back to the filesystem and updates the file modification time. Only those pages containing addr and len-1 succeeding locations will be examined.

Upvotes: 0

NPE
NPE

Reputation: 500357

This is OS- and architecture-specific, but most likely only the dirty page will be written to disk.

Upvotes: 1

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