[PATCH v3 1/2] Add ftruncate_file that truncates a struct file*

Tony Solomonik
2024-01-23T21:19:58Z

do_sys_ftruncate receives a file descriptor, fgets the struct file*, and
finally actually truncates the file.

ftruncate_file allows for truncating a file without fgets.

Signed-off-by: Tony Solomonik <tony.solomonik@gmail.com>
---
fs/internal.h | 1 +
fs/open.c | 51 ++++++++++++++++++++++++++++++---------------------
2 files changed, 31 insertions(+), 21 deletions(-)

diff --git a/fs/internal.h b/fs/internal.h
index 58e43341aebf..78a641ebd16e 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -182,6 +182,7 @@ extern struct open_how build_open_how(int flags, umode_t mode);
extern int build_open_flags(const struct open_how *how, struct open_flags *op);
extern struct file *__close_fd_get_file(unsigned int fd);

+long ftruncate_file(struct file *file, loff_t length, int small);
long do_sys_ftruncate(unsigned int fd, loff_t length, int small);
int chmod_common(const struct path *path, umode_t mode);
int do_fchownat(int dfd, const char __user *filename, uid_t user, gid_t group,
diff --git a/fs/open.c b/fs/open.c
index 02dc608d40d8..0c505402e93d 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -154,47 +154,56 @@ COMPAT_SYSCALL_DEFINE2(truncate, const char __user *, path, compat_off_t, length
}
#endif

-long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
+long ftruncate_file(struct file *file, loff_t length, int small)
{
struct inode *inode;
struct dentry *dentry;
- struct fd f;
int error;

- error = -EINVAL;
- if (length < 0)
- goto out;
- error = -EBADF;
- f = fdget(fd);
- if (!f.file)
- goto out;
-
/* explicitly opened as large or we are on 64-bit box */
- if (f.file->f_flags & O_LARGEFILE)
+ if (file->f_flags & O_LARGEFILE)
small = 0;

- dentry = f.file->f_path.dentry;
+ dentry = file->f_path.dentry;
inode = dentry->d_inode;
error = -EINVAL;
- if (!S_ISREG(inode->i_mode) || !(f.file->f_mode & FMODE_WRITE))
- goto out_putf;
+ if (!S_ISREG(inode->i_mode) || !(file->f_mode & FMODE_WRITE))
+ return error;

error = -EINVAL;
/* Cannot ftruncate over 2^31 bytes without large file support */
if (small && length > MAX_NON_LFS)
- goto out_putf;
+ return error;

error = -EPERM;
/* Check IS_APPEND on real upper inode */
- if (IS_APPEND(file_inode(f.file)))
- goto out_putf;
+ if (IS_APPEND(file_inode(file)))
+ return error;
sb_start_write(inode->i_sb);
- error = security_file_truncate(f.file);
+ error = security_file_truncate(file);
if (!error)
- error = do_truncate(file_mnt_idmap(f.file), dentry, length,
- ATTR_MTIME | ATTR_CTIME, f.file);
+ error = do_truncate(file_mnt_idmap(file), dentry, length,
+ ATTR_MTIME | ATTR_CTIME, file);
sb_end_write(inode->i_sb);
-out_putf:
+
+ return error;
+}
+
+long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
+{
+ struct fd f;
+ int error;
+
+ error = -EINVAL;
+ if (length < 0)
+ goto out;
+ error = -EBADF;
+ f = fdget(fd);
+ if (!f.file)
+ goto out;
+
+ error = ftruncate_file(f.file, length, small);
+
fdput(f);
out:
return error;
--
2.34.1