[PATCH 1/3] readfile: implement readfile syscall
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Date: 2020-07-04 14:03:04
Also in:
linux-fsdevel, linux-kselftest, linux-man, lkml
Subsystem:
filesystems (vfs and infrastructure), the rest · Maintainers:
Alexander Viro, Christian Brauner, Linus Torvalds
It's a tiny syscall, meant to allow a user to do a single "open this file, read into this buffer, and close the file" all in a single shot. Should be good for reading "tiny" files like sysfs, procfs, and other "small" files. There is no restarting the syscall, this is a "simple" syscall, with the attempt to make reading "simple" files easier with less syscall overhead. Cc: Alexander Viro <viro@zeniv.linux.org.uk> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- fs/open.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 50 insertions(+)
diff --git a/fs/open.c b/fs/open.c
index 6cd48a61cda3..4469faa9379c 100644
--- a/fs/open.c
+++ b/fs/open.c@@ -1370,3 +1370,53 @@ int stream_open(struct inode *inode, struct file *filp) } EXPORT_SYMBOL(stream_open); + +static struct file *readfile_open(int dfd, const char __user *filename, + struct open_flags *op) +{ + struct filename *tmp; + struct file *f; + + tmp = getname(filename); + if (IS_ERR(tmp)) + return (struct file *)tmp; + + f = do_filp_open(dfd, tmp, op); + if (!IS_ERR(f)) + fsnotify_open(f); + + putname(tmp); + return f; +} + +SYSCALL_DEFINE5(readfile, int, dfd, const char __user *, filename, + char __user *, buffer, size_t, bufsize, int, flags) +{ + struct open_flags op; + struct open_how how; + struct file *file; + loff_t pos = 0; + int retval; + + /* only accept a small subset of O_ flags that make sense */ + if ((flags & (O_NOFOLLOW | O_NOATIME)) != flags) + return -EINVAL; + + /* add some needed flags to be able to open the file properly */ + flags |= O_RDONLY | O_LARGEFILE; + + how = build_open_how(flags, 0000); + retval = build_open_flags(&how, &op); + if (retval) + return retval; + + file = readfile_open(dfd, filename, &op); + if (IS_ERR(file)) + return PTR_ERR(file); + + retval = vfs_read(file, buffer, bufsize, &pos); + + filp_close(file, NULL); + + return retval; +}
--
2.27.0