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lbutils/file: only support real pread/pwrite

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the portable version was written for fun, but
it's bloat, and makes the code hard to read.

every unix since about 2005 has these functions.

Signed-off-by: Leah Rowe <leah@libreboot.org>
This commit is contained in:
Leah Rowe
2026-03-31 12:22:42 +01:00
parent a769537554
commit 6d9f162f5b
4 changed files with 24 additions and 201 deletions
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util/libreboot-utils/lib/file.c
+16 -168
View File
@@ -160,9 +160,7 @@ err_fsync_dir:
ssize_t
rw_file_exact(int fd, unsigned char *mem, size_t nrw,
off_t off, int rw_type, int loop_eagain,
int loop_eintr, size_t max_retries,
int off_reset)
off_t off, int rw_type, size_t max_retries, int off_reset)
{
ssize_t rval;
ssize_t rc;
@@ -208,8 +206,7 @@ rw_file_exact(int fd, unsigned char *mem, size_t nrw,
off_cur = off + (off_t)rc;
rval = prw(fd, mem_cur, nrw_cur, off_cur,
rw_type, loop_eagain, loop_eintr,
off_reset);
rw_type);
if (rval < 0)
goto err_rw_file_exact;
@@ -247,180 +244,42 @@ err_rw_file_exact:
/* prw() - portable read-write with more
* safety checks than barebones libc
*
* If you need real pwrite/pread, just compile
* with flag: REAL_POS_IO=1
*
* A fallback is provided for regular read/write.
* rw_type can be IO_READ (read), IO_WRITE (write),
* IO_PREAD (pread) or IO_PWRITE
*
* loop_eagain does a retry loop on EAGAIN if set
* loop_eintr does a retry loop on EINTR if set
*
* race conditions on non-libc pread/pwrite:
* if a file offset changes, abort, to mitage.
*
* off_reset 1: reset the file offset *once* if
* a change was detected, assuming
* nothing else is touching it now
* off_reset 0: never reset if changed
*
* REAL_POS_IO is enabled by default in common.h
* and the fallback version was written for fun.
* You should just use the real one (REAL_POS_IO 1),
* since it is generally more reliable.
*/
ssize_t
prw(int fd, void *mem, size_t nrw,
off_t off, int rw_type,
int loop_eagain, int loop_eintr,
int off_reset)
off_t off, int rw_type)
{
ssize_t rval;
ssize_t r;
int positional_rw;
struct stat st;
#if !defined(REAL_POS_IO) || \
REAL_POS_IO < 1
off_t verified;
off_t off_orig;
off_t off_last;
#endif
int saved_errno = errno;
errno = 0;
if (io_args(fd, mem, nrw, off, rw_type)
== -1)
goto err_prw;
if (io_args(fd, mem, nrw, off, rw_type) == -1)
return set_errno(saved_errno, EIO);
r = -1;
/* do not use loop_eagain on
* normal files
*/
if (rw_type == IO_WRITE)
r = write_on_eintr(fd, mem, nrw);
else if (rw_type == IO_READ)
r = read_on_eintr(fd, mem, nrw);
else if (rw_type == IO_PWRITE)
r = pwrite_on_eintr(fd, mem, nrw, off);
else if (rw_type == IO_PREAD)
r = pread_on_eintr(fd, mem, nrw, off);
if (!loop_eagain) {
/* check whether the file
* changed
*/
if (check_file(fd, &st) == -1)
goto err_prw;
}
if (rw_type >= IO_PREAD)
positional_rw = 1; /* pread/pwrite */
else
positional_rw = 0; /* read/write */
try_rw_again:
if (!positional_rw) {
#if defined(REAL_POS_IO) && \
REAL_POS_IO > 0
real_pread_pwrite:
#endif
if (rw_type == IO_WRITE)
r = write_on_eintr(fd, mem, nrw);
else if (rw_type == IO_READ)
r = read_on_eintr(fd, mem, nrw);
#if defined(REAL_POS_IO) && \
REAL_POS_IO > 0
else if (rw_type == IO_PWRITE)
r = pwrite_on_eintr(fd, mem, nrw, off);
else if (rw_type == IO_PREAD)
r = pread_on_eintr(fd, mem, nrw, off);
#endif
if (r == -1 && (errno == try_err(loop_eintr, EINTR)
|| errno == try_err(loop_eagain, EAGAIN)))
goto try_rw_again;
rval = rw_over_nrw(r, nrw);
if (rval < 0)
goto err_prw;
if ((rval = rw_over_nrw(r, nrw)) < 0)
return set_errno(saved_errno, EIO);
if (rval >= 0 && !errno)
errno = saved_errno;
return rval;
}
#if defined(REAL_POS_IO) && \
REAL_POS_IO > 0
goto real_pread_pwrite;
#else
if ((off_orig = lseek_on_eintr(fd, (off_t)0, SEEK_CUR,
loop_eagain, loop_eintr)) == (off_t)-1) {
r = -1;
} else if (lseek_on_eintr(fd, off, SEEK_SET,
loop_eagain, loop_eintr) == (off_t)-1) {
r = -1;
} else {
verified = lseek_on_eintr(fd, (off_t)0, SEEK_CUR,
loop_eagain, loop_eintr);
/* abort if the offset changed,
* indicating race condition. if
* off_reset enabled, reset *ONCE*
*/
if (off_reset && off != verified)
lseek_on_eintr(fd, off, SEEK_SET,
loop_eagain, loop_eintr);
do {
/* check offset again, repeatedly.
* even if off_reset is set, this
* aborts if offsets change again
*/
verified = lseek_on_eintr(fd, (off_t)0, SEEK_CUR,
loop_eagain, loop_eintr);
if (off != verified) {
errno = EBUSY;
goto err_prw;
}
if (rw_type == IO_PREAD)
r = read_on_eintr(fd, mem, nrw);
else if (rw_type == IO_PWRITE)
r = write_on_eintr(fd, mem, nrw);
if (rw_over_nrw(r, nrw) == -1)
break;
} while (r == -1 &&
(errno == try_err(loop_eintr, EINTR) ||
errno == try_err(loop_eagain, EAGAIN)));
}
saved_errno = errno;
off_last = lseek_on_eintr(fd, off_orig, SEEK_SET,
loop_eagain, loop_eintr);
if (off_last != off_orig) {
errno = saved_errno;
goto err_prw;
}
errno = saved_errno;
rval = rw_over_nrw(r, nrw);
if (rval < 0)
goto err_prw;
errno = saved_errno;
return rval;
#endif
err_prw:
return set_errno(saved_errno, EIO);
}
int
@@ -501,17 +360,6 @@ if_err_sys(int condition)
return 0;
return 1;
}
/* errno can never be -1, so you can
* use this to conditionally set an integer
* for comparison. see example in lseek_on_eintr
*/
int
try_err(int loop_err, int errval)
{
if (loop_err)
return errval;
return -1;
}
int
fs_rename_at(int olddirfd, const char *old,