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authorEric Biederman <ebiederm@xmission.com>2009-02-18 17:48:16 -0500
committerLinus Torvalds <torvalds@linux-foundation.org>2009-02-18 18:37:53 -0500
commit8f19d472935c83d823fa4cf02bcc0a7b9952db30 (patch)
tree25cabc0b48ad0acb05fa69f92de617cf588fec8d
parent55ec82176eca52e4e0530a82a0eb59160a1a95a1 (diff)
seq_file: properly cope with pread
Currently seq_read assumes that the offset passed to it is always the offset it passed to user space. In the case pread this assumption is broken and we do the wrong thing when presented with pread. To solve this I introduce an offset cache inside of struct seq_file so we know where our logical file position is. Then in seq_read if we try to read from another offset we reset our data structures and attempt to go to the offset user space wanted. [akpm@linux-foundation.org: restore FMODE_PWRITE] [pjt@google.com: seq_open needs its fmode opened up to take advantage of this] Signed-off-by: Eric Biederman <ebiederm@xmission.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Paul Turner <pjt@google.com> Cc: <stable@kernel.org> [2.6.25.x, 2.6.26.x, 2.6.27.x, 2.6.28.x] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/seq_file.c36
-rw-r--r--include/linux/seq_file.h1
2 files changed, 33 insertions, 4 deletions
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 5267098532bf..a1a4cfe19210 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -48,8 +48,16 @@ int seq_open(struct file *file, const struct seq_operations *op)
48 */ 48 */
49 file->f_version = 0; 49 file->f_version = 0;
50 50
51 /* SEQ files support lseek, but not pread/pwrite */ 51 /*
52 file->f_mode &= ~(FMODE_PREAD | FMODE_PWRITE); 52 * seq_files support lseek() and pread(). They do not implement
53 * write() at all, but we clear FMODE_PWRITE here for historical
54 * reasons.
55 *
56 * If a client of seq_files a) implements file.write() and b) wishes to
57 * support pwrite() then that client will need to implement its own
58 * file.open() which calls seq_open() and then sets FMODE_PWRITE.
59 */
60 file->f_mode &= ~FMODE_PWRITE;
53 return 0; 61 return 0;
54} 62}
55EXPORT_SYMBOL(seq_open); 63EXPORT_SYMBOL(seq_open);
@@ -131,6 +139,22 @@ ssize_t seq_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
131 int err = 0; 139 int err = 0;
132 140
133 mutex_lock(&m->lock); 141 mutex_lock(&m->lock);
142
143 /* Don't assume *ppos is where we left it */
144 if (unlikely(*ppos != m->read_pos)) {
145 m->read_pos = *ppos;
146 while ((err = traverse(m, *ppos)) == -EAGAIN)
147 ;
148 if (err) {
149 /* With prejudice... */
150 m->read_pos = 0;
151 m->version = 0;
152 m->index = 0;
153 m->count = 0;
154 goto Done;
155 }
156 }
157
134 /* 158 /*
135 * seq_file->op->..m_start/m_stop/m_next may do special actions 159 * seq_file->op->..m_start/m_stop/m_next may do special actions
136 * or optimisations based on the file->f_version, so we want to 160 * or optimisations based on the file->f_version, so we want to
@@ -230,8 +254,10 @@ Fill:
230Done: 254Done:
231 if (!copied) 255 if (!copied)
232 copied = err; 256 copied = err;
233 else 257 else {
234 *ppos += copied; 258 *ppos += copied;
259 m->read_pos += copied;
260 }
235 file->f_version = m->version; 261 file->f_version = m->version;
236 mutex_unlock(&m->lock); 262 mutex_unlock(&m->lock);
237 return copied; 263 return copied;
@@ -266,16 +292,18 @@ loff_t seq_lseek(struct file *file, loff_t offset, int origin)
266 if (offset < 0) 292 if (offset < 0)
267 break; 293 break;
268 retval = offset; 294 retval = offset;
269 if (offset != file->f_pos) { 295 if (offset != m->read_pos) {
270 while ((retval=traverse(m, offset)) == -EAGAIN) 296 while ((retval=traverse(m, offset)) == -EAGAIN)
271 ; 297 ;
272 if (retval) { 298 if (retval) {
273 /* with extreme prejudice... */ 299 /* with extreme prejudice... */
274 file->f_pos = 0; 300 file->f_pos = 0;
301 m->read_pos = 0;
275 m->version = 0; 302 m->version = 0;
276 m->index = 0; 303 m->index = 0;
277 m->count = 0; 304 m->count = 0;
278 } else { 305 } else {
306 m->read_pos = offset;
279 retval = file->f_pos = offset; 307 retval = file->f_pos = offset;
280 } 308 }
281 } 309 }
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index 40ea5058c2ec..f616f31576d7 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -19,6 +19,7 @@ struct seq_file {
19 size_t from; 19 size_t from;
20 size_t count; 20 size_t count;
21 loff_t index; 21 loff_t index;
22 loff_t read_pos;
22 u64 version; 23 u64 version;
23 struct mutex lock; 24 struct mutex lock;
24 const struct seq_operations *op; 25 const struct seq_operations *op;