O_APPEND, lseek() and pwrite()

[Timo Sirainen <tss@iki.fi>]

If I open a file with O_APPEND and write() to it, it looks like the  
file offset is updated and I can get it with lseek(SEEK_CUR). Can I  
trust that this behavior won't change in future Linux versions?  
Apparently this isn't standard, because at least OS X and Solaris  
don't do this.

pwrite() ignores the file offset if the fd has O_APPEND set (with  
2.6.20). http://www.opengroup.org/austin/mailarchives/ag/ 
msg09453.html suggests that it shouldn't ignore it. Could this be  
changed? For now I can of course just change the flag with fcntl().

I guess there aren't any limits to how large blocks write() accepts  
without the data being mixed with another process's writes (both with  
O_APPEND)? And I guess there aren't any horrible performance problems  
with this, so that this is actually a good idea compared to file lock  
+ write() + unlock? :)

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