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Subject2.4 sendfile() not doing as manpage promises?
Hi everybody,

I tried to use sendfile() to send data from a tcp/ip socket to a file on
disk. This does not work, giving EINVAL.

Using the very fine kgdb product (http://kgdb.sourceforge.net) and my laptop
for remote debugging, I was able to trace this to this:

sys/filemap.c::sys_sendfile():

if (!in_inode->i_mapping->a_ops->readpage)
goto fput_in;

After some exploring with 'ddd' (a very nice graphical frontend for gdb,
which includes tools to display and traverse structs), I found that this
probably means that sendfile() can only be used to send files from
blockdevices which support mmap()-like functionality.

Is this correct? In that case, the wording of the manpage needs to be
changed, as it implies that 'either or both' of the filedescriptors can be
sockets.

Regards,

bert hubert

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