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Amend File_system session with SEEK_TAIL support

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Used to read or write from the end of a file when multiple packets may
be in transit.

Supported by ram_fs, rump_fs, and vfs servers.

Fixes #1775
This commit is contained in:
Emery Hemingway
2016-04-26 16:28:07 +02:00
committed by Christian Helmuth
parent b38c5006d8
commit 52cc50174f
4 changed files with 59 additions and 15 deletions
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22
repos/os/src/server/vfs/node.h
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@ -128,6 +128,7 @@ class Vfs_server::File : public Node
private:
Vfs::Vfs_handle *_handle;
char const *_leaf_path; /* offset pointer to Node::_path */
public:
File(Vfs::File_system &vfs,
@ -140,7 +141,8 @@ class Vfs_server::File : public Node
unsigned vfs_mode =
(fs_mode-1) | (create ? Vfs::Directory_service::OPEN_MODE_CREATE : 0);
assert_open(vfs.open(path(), vfs_mode, &_handle, alloc));
assert_open(vfs.open(file_path, vfs_mode, &_handle, alloc));
_leaf_path = vfs.leaf_path(file_path);
}
~File() { _handle->ds().close(_handle); }
@ -160,6 +162,15 @@ class Vfs_server::File : public Node
{
Vfs::file_size res = 0;
if (seek_offset == SEEK_TAIL) {
typedef Directory_service::Stat_result Result;
Vfs::Directory_service::Stat st;
/* if stat fails, try and see if the VFS will seek to the end */
seek_offset = (_handle->ds().stat(_leaf_path, st) == Result::STAT_OK) ?
((len < st.size) ? (st.size - len) : 0) : SEEK_TAIL;
}
_handle->seek(seek_offset);
_handle->fs().read(_handle, dst, len, res);
return res;
@ -169,6 +180,15 @@ class Vfs_server::File : public Node
{
Vfs::file_size res = 0;
if (seek_offset == SEEK_TAIL) {
typedef Directory_service::Stat_result Result;
Vfs::Directory_service::Stat st;
/* if stat fails, try and see if the VFS will seek to the end */
seek_offset = (_handle->ds().stat(_leaf_path, st) == Result::STAT_OK) ?
st.size : SEEK_TAIL;
}
_handle->seek(seek_offset);
_handle->fs().write(_handle, src, len, res);
if (res)